Charging without rendering service to customers just because they signed a contract!

Apparently they charged me for services they never rendered, I signed up a contract with them where they were supposed to give me 40GB day and 40GB during night. After a day of receiving the SIM cards I inserted them and they were not working, tried them after a month but still they were not working, the nearby branch was offline so I couldn’t be assisted I sent them emails but still the SIM cards weren’t working! Then I just kept the SIM cards, after 3/4 months I was handed over because the account that was in arrears of about R1900. I asked for which MTN number? They can’t tell; why should I pay for services I never received?