Incomplete conversion of Cellphone Contract to Prepaid

I have had a cellphone contract via my previous company for many years. I decided to convert the contract to prepaid. Immediately thereafter, I decided to port the number to Afrihost due to their cost effective voice calls. The number wont port because on Afrihost side, the number appears to be a MTN contract number. MTN insist that it is a Afrihost issue which clearly is not. This has been going on for almost a year and I am running out of options. MTN, please tell me what I should do to have this resolve. My next option is to contact ICASA.