*******ion on my cell phone account

I took out a new contract with the request to keep my old number. I have been informed to do a sim swop by the assistant. A few weeks later we realized it is not going to work, and requested to cancel the contract. After a few weeks waiting from in-store assistance, the lady informed us the request was declined. My cell phone stopped working that same day and I made a visit to in-store. They said there is network problems with certain numbers and that can be the cause why my number wasn't working, and to give it 24 hours to resolve. That same evening my daughter said when she called me on that number a stranger (male) is answering. The next day 05Jun, I went in-store again and reported. The assistant said there was a BIS activated on my number few min ago, although I have the sim with me (not even inserted in a device). After numerous calls and request for the store manager to assist, the manager said to her personnel to solve the problem themselves. after few calls to head office today, they said this is a in-store problem to be fixed. Where to now? I am paying for someone else using my account, where I lost all my data and inconvenience to solve my problem with a useless system.