No sim swop activation after a week

Last weekI upgraded two contracts with cell c. I received the new phones on Friday with the new sims due to the new phones taking smaller sims. Cel C managed to know that the new phones require the sims,, but even after 5 calls to the cellc customer care to date and plenty of empty promises, I cant get the new sims activated via simm swop. I will probably still get a full months bill even after the firts quarter is gone. Ive had it ,,,How do I cancel CellC?