They only debit only when it suits them

I have a contract which is due to expire july next year. The problem is the stopped debiting my account with no explanations. I tried to make manual payments but sometimes I forget. Im well aware that I am behind with payments but as to how much I dont know I tried to email them as per refference number 000-xzsc with no response from them. I wish to negotiate the amount that I am behind with. When I go to the store im told I should phone accounts department they dont do it for me.the problem is they do debit one month the next they dont im confused now