You're using all your CDs at once. You clearly aren't good enough to pull threat, that means you're provoking off the better tanks. Don't.

If it was one person who had an issue with you, I would say they were being a dick. However, it sounds like the majority of the alliance had an issue with you. That means YOU are the issue.

If you don't have a basic understanding of what is required of you in any level of content do some research before you join it. It is not the responsibility of 23 other people to hold your hand because you were too lazy to Google something like "ffxiv alliance raid tanking explained". No one is asking you to watch entire videos or strategies. Just know wtf you're supposed to do as a tank.

In addition, it sounds like your gear sucks. Alliance raids are a joke, even the newest one. If one healer struggles to keep you up, it's the healer or your gear. When multiple healers can keep you up, it's definitely you and youe gear.

Read. About. Your. Class. And. Role. Other players are there to help, not do most of the work for you.