not happy with latest invoice

I am writing again, I wish that I could be bought out of my contract with cellc, I upgraded my data contract with you, I was not informed that I can get a tablet with this data contract neither that I will have to pay extra this month R299, I have been paying R118.98 every month, when I called last week to enquire about the invoice I was made aware that the discounts has been taken off, I told the agent when I done the upgrade I specifically asked will my subscription stay the same I was assured it will remain R118.98 now what a shock I must pay R299 I told the agent last week I will return this amount & just pay the R118.98, I honestly don't have words for the service I am receiving from cellc, I just want out.