Aren't they saying that the sum has been increased because you went to POPLA?
Well, it is not that simple.
Beavis didn't say they couldn't levy their collection costs. If they go to court they certainly can.
Beavis just said that the challenge that £85 didn't represent loss was wrong.
In fact, they usually do ask for a greater sum if you appeal. That may or may not succeed in court but it doesn't amount to unlawful harassment. They are chasing in a debt. That may well be misconceived but it isn't harassment.
If that were to be accepted then any wrongful claim would be an instance of harassment.
If you have paid in full then just ignore them and invite them to sue. It will get nowhere even if they do.
Can I clarify anything for you?
I'm not sure for what?
They are just bringing an incorrect debt collection action. You cannot sue for that.
I suppose the only thing you could do is seek an injunction but that would cost in the low hundreds and you won't recover.