Bt

Krispy1_2

I have a bt landline which i pay 11 pounds a month so i can get internet. During the first few months i had it, bt made a mistake and put me under the wrong package and told me that i would have to pay 150 pounds to swap it back over. I pointed out the mistake and after three attempts to direct debit this money they refunded the money. Recently i got a bill through from them telling me that i have to pay them 200 pounds because someone made a mistake and refunded me too much. I told them that its there mistake but they have told me that i have to pay this money in the next 2 months. I am only a student nurse and cannot afford there mistake. I have asked to be called back by their supervisor. What rights do i have and can anyone give me advice? i feel like their trying to intimidate and extort me for money