Migrated to Prepaid - Still Receive Statements

My contract ended at the end of October 2015. MTN Call Centre advised me to call in the day after my contract expired to migrate my account to prepaid. A call centre agent advised me that there is still an outstanding amount that needs to be paid and it will take 2 days after payment is done to reflect so I need to follow up with the call centre again, which I have done. To my surprise at the end of February I received a bill of approximately R530-00. The number has not even been in use since October 2015. I contacted the call centre again to question this, by which they referred me to Legal Department because the account was handed over. I requested to speak to a legal representative and was unsuccessful as they couldn't transfer me. But they informed me that Legal department will get back to me. Two weeks later someone called from legal informing me that she is not able to assist me & referred me back to the migration department. I've been battling for 1 and 1/2 months to get someone to assist me. Yesterday morning I spoke with another agent & requested to speak to a superior but with no luck. She took my details saying someone will contact me. I haven't heard from anyone since.