Transfer of ownership not done, and now i sit with the bill

I sold a restaurant end January 2014 and paid the Telkom account up to date at the time. Also went into Telkom shop at Greenstone Mall and handed in the transfer of ownership forms. A while later I received a demand from Telkom for outstanding balance on the restaurant phone bill, so I took a trip back to Telkom shop to try and figure out why I was being asked for the money. It was not possible to get a printout from them, but from screen shots on their system, it is apparent that the transfer was done to the new owner, but that they kept my ID number on the system. The "First installation date" is recorded as after that date of sale, and after my final invoice from Telkom (that I had paid). I have just received a final demand from the third debt collector in the past three years, and I would really like to get this matter resolved.