Consulting called me...

Consulting called me from mondo offered me 1 data Sim with 10GB for R99,then she sent 2 Sim,1 Sim had 6gb another with 4gb,now I called them a said they will investigate and they blocked both Sim,I didn't use them,now I ended canceling the contract because it was a process for them to try to fix the Matter, I asked them to cancel the contract which mondo did cancel,but the problem now is the didn't communicate with the service provide which is mtn,they kept sending invoices,now I contacted mtn trying to find out why are they billing me,they explained and I told them my side of the story and they said they do realize the fault was with mondo for not communicating,can I please be assist,because as I said before my credit record it's affected by this