Cancel Contract

I have a contract with MTN that expire in March 2020, but I lost my business house car, basically everything I only get my Sassa Pension R1780 per month, I have requested MTN if they please can cancel my Contract that is R1320 pm so I can get a cheaper package or pay as you go, they refuse point blank and said I have to stay and if I don't pay they will take legal action against me, what can I do