I wonder how many people have this same complaint

I did a subscription with Jacklin Enterprises for the Ultimate Marvel Graphic Novel series of books for one of my godsons. The books are numbered, but were not sent in chronological order. After two years and about 60 books received, they suddenly started sending books from a different series. After getting nowhere with queries as to why, I cancelled the subscription. All the books received had been paid for, despite the fact that this included 10 unwanted ones. A while later I received an account for R439,80 from Jacklin. Countless requests for a final statement explaining the outstanding amount were refused by Jacklin, and in September 2015 I gave up trying, stopped receiving accounts and assumed they realised they had erred. Today I received a call from a debt collection agency demanding I pay Jacklin an amount of over R700. How on earth can a company deny a final statement to prove their claim is legitimate??