MTN so called 'service provider'

How can you as MTN increase my monthly instalment after I signed a contract stating NOTHING about increases for 24 months and now you say it is because of the VAT. I signed a contract with MTN, not the government! And this expiry of data is also BS! When I asked the consultant how she would feel if her service provider expires her data she didn't even want to answer me, probably to afraid she will lose her job as the call is recorded. I will find an article from the consumer law to prove that MTN is in the wrong.