Car insurance overpayment refund

[Lola49]

I have a question, I took out a one year car insurance for my daughter as a learner driver on her car. 15 days later she passed her test, I had paid for the policy in full. The policy has reference to a 14 day cancellation - but we were less than a day over this. To add more confusion, they gave a refund of more than we had paid in the first place - which of course we have offered to pay back. The full policy costed £335 - I am saying that we would happily pay back £66. for the 2 weeks that we had the policy for, they want £139. I have asked for a breakdown of costs but they won't give this - they have just argued that they have overpaid on the refund (they did). My question is, do we have to pay back any money given that it was actually their mistake with the refund, and 2. What rights does my daughter have with saying that she wants to payback the £66 only given we were just outside of the 14 day cancellation period, I think by less than half a day?
They are saying that they are passing the debt to bailiffs rather than negotiating with us. My daughter isn't now living with us as she has gone to university.

[des8]

Firstly you have to refund any money over refunded in error.

Your insurance policy will state the proportion of premium the insurers require if the policy is cancelled prior to expiry date.
Most companies now use pro rata terms some also charge a cancellation fee
As you were outside the 14 day cooling off period (even if only by one day) the insurance terms will kick in.

If this policy was placed through an intermediary, they might also be charging an "administration" fee