This is a normal reaction because you have been overusing it, and at a high percentage as well. I use Epiduo (Adapalene 0,1% + Benzoyl Peroxide 2.5%) and I understand the burning sensation with moisturiser and itchy neck.

What you need to do is completely stop using it until your skin calms down (i.e. your skin stops burning when putting on moisturiser). Then, make sure your moisturiser doesn't contain any exfoliating acids (glycolic, lactic or salicylic). Keep your routine simple and consistent. Use a gentle cleanser 1-2 times a day, moisturise 1-2 times a day with a moisturiser for sensitive skin preferably, and sunscreen in the daytime.

Once your skin is back to normal, start using BP, at 2.5%. You will do Short Contact Therapy with it. This means you cleanse your face at night with your cleanser, pat dry, then apply a small amount of BP to your face/affected areas and wait for 5 minutes. Then wash it off with water and moisturise. The next night, repeat the process, but this time leave it on for 10 minutes. Then the next night for 20 mins, 40 mins, 1 hr, then overnight.

Sun protection is very important when using acne medication, as BP especially can make you more susceptible to sunburn. SPF30 and above is good. Hope this helps and good luck