signed contract differs from online contract

Hi all<br> <br> <br> <br> I need some help, I took out a telkom contact and migrited my contract a few months later to a diferent phone, on my signed contract it states that I can pay the outstanding amount on the phone for the firts contact with my new contract, a month later I got a bill where they took off a amount of R6000.00 from my bank account for the migration fee for the previous phone, after caling in they told me my signed contract is not falid and it was a instore consultants fault and I will pay that amount in full, what must I do? i evntaully paid the full amount just for telkom to stop naging abount it, the consultant told me insture that , \ oops, he made a computor error and captured it incorrectly\" after I paid the R6000.00 2 days later Telkom took another R2000.00 from my account for no reason, no I have a debt collector from telkom calling me for the R2000.00 I reveresed, what must I do to get these people to stop arrasing me??"