What a nightmare

This company is such a nightmare to deal with. I have been paying my contract perfectly and on time with no missed payments for the duration of my contract. 2 months before my contract was due to expire I tried to upgrade. Received no assistance. When it had expired I tried to cancel, they begged me not to cancel and they would migrate me to another option. That never happened. Instead My invoice amount has gone from R269 to R1000 for 30GB of data a month? I would just like assistance please, to either cancel my contract or let me upgrade. Dealing with MTN has been the worst experience of any service provider I have ever dealt with.