Poor service on doing swimswap

I have a very bad experience with MTN and to be honest i will never use this network again. I had a contract phone with them and about three weeks ago i paid off the contract and terminated it. Now i am on prepaid not contract. Last week Monday I lost my phone and now I need to do a swimswap and still use my number but instead of helping me they are telling that my number is between contract and prepaid but how is that my problem? Why cant the technicians sort that out? I have been to the Tygervalley mall store in Cape Town more than 3 times already and they telling me this lame excuse that does not make sense. on the other side their contract people are saying the number is on prepaid and they should be able to do a swimswap at the store.