Appalling Inaction from RCS, QUEENSPARK & VVM

I a beyond frustrated. I get constant harrassing calls from various collection agencies representing RCS/Queenspark demanfing payment from me, in spite of my having settled the account in full in September last year & sending proof of payment to them as requested by VVM, their appointed collectors at the time. VVM have also proven to be most unhelpful, saying that they're no longer the RCS appointed agents & cannot assist me. Nice, harass me, take my money then wash your hands off me when I ask for assistance. All of this has compromised my credit rating. Appalling behavior, lack of management by all 3 companies.