Welcome to the community and thanks for your post!
I'm sorry you have had such a difficult time changing the date your payments are debited from your account. I have went over all the points you have raised and I have to admire your patience as if the same thing happened to me I wouldn't be as calm as you to be honest.
Can you send us over your details and we'll give you a hand to sort everything out from here? Click on my username here >> RobbieMac << and you'll see our contact link underneath my profile picture.