A debt collection agency can charge fees over and above what you owe, but only if you were told about those fees at the time that you bought the hire-purchase goods or got the loan. The fees must be reasonable.
If you’re not happy about the fees you’ve been charged, you can ask the debt collector to explain them. You can also compare them to what other debt collection agencies charge. If you think the fees aren’t reasonable, you can apply to the Disputes Tribunal and ask it to reduce the fees (see the chapter “The Disputes Tribunal”).