Vodacom Upgrade wrong amount

I am a few years at vodacom and this is my first serious complaint. i upgrade at garden route mall at end of 2017. i upgrade and budged for contract of R170 per month because i dont want it to be high , i already got other contracts also. when my first invoice of R340 come they told me the cheap device i took was also R170 with my contract . I said no i sign just for a monthly contract of R170 and nothing more. Vodacom freeze my account and make it pay as you go. A few months later my bill is R2800. I tried the customer care a few times explain everything and said where is my benefits every month since i didnt get any minutes or data. They said they will sort it out and now my contract is suspended. Very poor service and i am tired of customer care because it seems they didnt care.

Kind Regards