Have trying since 2014 to resolve billing issues

I sent emails, made phone calls and nothing is resolved. Eventually MBDCS started contacting me and they are even worse and are also not responding to emails and cannot resolve the issue via phone either. PLEASE I have been struggling since last year to have mistakes corrected and I just keep being informed that I owe money that I don't as my account was paid up when I cancelled my contract. The contract was cancelled on the system the following month after my notice was already received within the notice period so I kept being charged and interest added while my complaint goes unresolved.<br>