DMC making life hell

This DMC is really making my credit life hell. I lodged a dispute with Experian, only to be told that according to DMC's records, my debt hasn't prescribed as I'm 9 months in arrears. How can I be in arrears for a debt I haven't paid? These accounts have been active since June 2018. I then referred the matter to Credit Ombud and they said that I could not be helped because DMC is not their member.