Paid up account handed over to another collections company.

I'm sick and tired and I don't know who to call. Cell C handed me over to MMM Capital to pay an outstanding amount, which I did . I've requested a paid up letter from them, but now all of a sudden their emails and contact numbers don't exist. Now MBD is harrassing me with phonecalls and emails. I'm in contact with a legalwise consultant and will not stand for this nonsense anymore