Your ex-wife literally does not have the right to solely speak for the feelings of your kids, whose feelings are definitely more complicated than what she says.

Don't blame your 15 year old either, who is probably being used by her mom to attack you and your new wife. However, I disagree that your kid has no say about your problems and she was involved by being there. No, she's not an adult, you're right. Talk about this with a good family therapist and then discuss it again with your teen, with the therapist there if you need it. Nothing like saying sorry and saying that they were right, if you believe it, for making most teens feel better.

You give no information about your custody arrangement--please add that to your OP--but you need to be very careful and at least speak with your attorney by phone first thing Monday, because:

-ex denied you visitation for the whole weekend, which is illegal;

-ex denied you contact by phone, which is illegal;

-she spoke badly with hate words about your SO, which is not allowed;

-she apparently lied about who your new wife is or what she has done and said she had a bad character, which is not allowed.

Get your attorney to notify the court immediately about your ex's illegal pulling of visitation and also ask for it to be replaced by equal visitation ASAP.

BUT ex could also try to get YOU in trouble for HER unilateral cancellation of your visitation by claiming you missed visitation, or by trying to make you pay her more money, because normally you feed them during visitation, etc.

Why did ex do this now? Does she have a new attorney? Was it a birthday she wanted to have with the kids?

If ex continues this behavior, enough missed (even involuntary) visitation by you can trigger a new court visit and court order or a ruling by a guardian ad litem if you have one, to alter the visitation orders and decrease YOUR visitation.

Going out strongly on this, taking away visitation, which is illegal, you must also stop the bigotry here. If your current attorney can't handle it, get a new one. You can also reach out to the American Civil Liberties Union or racial rights groups or legal clinics, who may provide you with free additional legal help but you will need to be very persistent and let everyone know you are trying to stop this NOW.

Also, family therapy with your kids and new wife and you is very important ASAP. Ask to get it scheduled right away through your attorney and the courts, in addition to your usual visitation time if possible. However, listen to your attorney if he or she has an alternate solution.

If your state allows recording, record your ex's anti-racial statements as evidence. In some states, if you yourself are a party in the conversation, you are allowed to record. Often, in other states, if you inform the other person you are recording, you can then record legally--but check your state law. There's no point in doing this if you can't play it for your attorney, ex's attorney and the judge. Remember when talking to ex, she might start recording you too.

Save ex's emails, im's, letters, etc.

Save your child/children's emails and im's, etc. carefully as proof.

Hopefully, you can get the conversation/words used/visitation calmed down here. If you have a strong attorney and you can be persistent, your ex is damaging her chances at increasing her custody: she may end up having less custody because of her outrageous attempts at parental alienation and outright racism. Anti-racial and damaging speaking by the ex, who is the other custodial parent, may be getting into illegal behavior, but again states differ and ask your attorney.

If this has been going on a while, put all your notes and calendars together as proof, written at the time as much as possible. Fill in the gaps as best you can from memory. Be honest and clear. From now on, keep a written record with days, times, times of calls, phone calls denied, visits shortened or denied, wording of ex's claims about the what the kids supposedly said like "they don't want to see you," insulting statements made by ex about you and insulting and racial statements by ex about your wife, etc.. It seems that there is already proof from what you say here that makes it clear that ex is teaching your own kids to be prejudiced against their stepmom and their new sibling. This is the kind of thing that needs to be made completely clear that it has been happening, it needs to be completely taken care of ASAP with therapy and calm family talks, and stopping your visitation cannot be ignored. Call your attorney first thing in the morning.

So sorry, OP! Good luck.