I don't know. You need to write and make a formal complaint.
Ask for a statement of account. You are entitled to this. You can see what they have and have not applied.
Once you have this then you can dispute it.
If if it disputed then you can complain to the Financial Ombudsman. They regulate these firms and can investigate the complaint (if its a regulated loan).
They can do this at: www.financial-ombudsman.org.uk
If that does not work then you can refuse to pay.
They can only make you pay if they issue proceedings. You can then argue the point before the Judge.
But ask for a full breakdown of costs and statement of account.
Once you have that, you know where you stand.
Can I clarify anything for you about this today please?
If not I would appreciate a 5 star rating for my answer. If you need more help, you can ask follow up questions for free and I would be delighted to assist. Thanks!