Cartrack nightmare

I had an account with cartrack and my account had arrears and i made a payment arrangement with them. They keep on calling me asking me to pay them despite the payment arrangement still debiting my account. Furthermore Cartrack debits my accounts when they please , not according to the payment date that I agreed on. In one calendar month they run at least 3 debit orders. Despite this the account balance does not go down, its forever increasing the arrears. I have requested for the copy of my contract with them including a copy of the payment arrangement , they refuse me give me the copy of the contract , they always say i will receive the copy but i never receive it .