BLITZ FIBRE - CELL C

I have a contract with Blitz Fibre cell C for 15/15 mg line @R799 pm. Then two months ago I received a mail from Cell C informing me that Blitz had been taken over by Vox Frog Foot and my package will remain the same. A month later I received another email from Cell C stating that my line would drop to 10/10mg for R799 pm, this is unacceptable to pay the same amount for a slower line when I have a contract with them! I have sent several mails to Cell C and have not received any reply.