Poor handling of *****ulent account anddebt handover to an *********** debt collecting firm

I have been contacted by Nimble Group for an outstanding account with Cell C with an outstanding amount in excess of R4000. This account was opened *****ulently using my name, yet this is the first time I hear of such an account. How can Cell C appoint an *********** debt collector that doesn't do proper checking before expecting me to pay up? Now I have to prove that it was not me that opened the account! I read another user's pains in getting such a matter resolved, and I'm not prepared to go through the same trouble, I expect Cell C to correct their records and correct this matter with Nimble Group.