Tired of MTN contract

I took a contract phone with MTN and they gave me a cellphone, with 3 sim cards. The cellphone only accept one sim card. I told them I do not need other sim cards and I was told they were going to bill me for all three, even if I do not use the sim cards. And I was asked to Rica the Sim cards and I have been struggling to Rica them. Every MTN store I go to I am told that the system is down. When I called their call centre I was told that if I am not happy I should return back the cellphone. But the MTN stores are refusing to take the cellphone and de activate my contract. Even the cellphone they gave is me is low and freezing everytime, the phone is HISENSE F20.