I skip 2 months of payment

I skip 2 months of payment. Then, September, I paid back .but when I sent Payment I made a mistake I put a wrong reference I contacted they told me I must send a proof of payment on their email address that I was given..I even made a follow up. On it now, I received sms from they lawyers that they took my account to credit berue. They never told me if they received my email or not .I am not happy with their service .I tried so many times to cancel they contract it not possible.