Unable to change contract number

Hi,<br> <br> I want to change my current number of my top up account to my original vodacom number. Since I got this number, I have been bombarded with calls and smses of the previous owner of this number. The previous owner didn't pay accounts and owed a lot of people. Now, its been more than 2.7 years this has been happening and is not stopping. I can't take it anymore. I don't want to leave my contract or end it as I enjoy and benefit a lot from it. However, I can't take the calls and smses anymore. I called the call centre and they told me it can't be done for topup. What should I do? Endure these calls? is it fair? I am stuck, if I end this contract and take a new one it will cost me a lot. Am stuck UNHAPPY here. Should I switch to cell C and have them buy out this contract? that seems affordable...