bad payer due to Damelin

I did some studies through damelin correspondence college. Due to the poor service and procedures I had to cancel my studies with them. I done everything requested from me such as sending a written request to cancel and gave in the textbooks but 2 years later I encounter problems when trying to get a phone contract because damelin listed me as a bad payer with ITC. I request that damelin confirm in writing that I do not owe them and the it was cancelled so I can clear my name with ITC but the *********** call centre agents avoid solving problems by dropping my calls. This is the worst service I ever received and if this is not sorted by Monday 09/03/2015 I will take it as far as possible.