DSTV not honouring promotional agreements

I was sent a special offer to pay a reduced rate for 6 months if I re-activate my DSTV Streaming package. It was a battle for 2 weeks to get DSTV to get all the services activated and up and running. Now in the second month instead of the promotion rate we agreed upon, they billed me the full amount for a DSTV streaming package. I don't want the additional amount I paid to sit in my account with DSTV as credit. I want the refund in my account.