In reply to dh73:
Potentially a dangerous approach, small claims no, but a default on an individuals credit file yes.
I had a situation probably 10 years ago, I decided to change my mobile phone provider, paid what was due and moved on. I received another bill, which I challenged and they where unable to explain on the phone. I asked them to provide an explanation in writing as to why I had received this additional bill (it was only about £22).
I didn’t hear anything, then a few months later a got a letter from a collection company. I rang them and said that this was part of an unresolved challenge and that they had no right to seek any money from me. The collection company wrote to me and said that they had checked with the phone company and that I was correct that the matter had been handed back to the phone company. I heard no more.
A year later, I applied for a personal loan and was very surprised to by turned down. I checked my credit file and found that the phone company had marked my file with a default. I took some advice and after a few months of increasingly threatening correspondence they removed the black mark without admitting fault. No lasting damage to my credit file, but it cost me money and quite a lot of time and inconvenience.