Who is RMCS??

I got a Cellc Simcard when they first started operating, bought it from a Pep store. I receive SMS's from Cellc saying that I qualify to upgrade, but my number isn't registered with them. From Friday I have had no coverage on my CellC Simcard, just to be informed by CellC that my Simcard is registered with RMCS. I have never heard or had any dealings with RMCS. I don't have a contract phone, which according to CellC I do have. If anybody from RMCS can please clarify this for me I would be happy, otherwise I will just be angry......