Hi Colin
We advise claimants to get the timing right when applying for UC as you can loose out. We would advise that claimants apply for UC just after getting their ESA payment.
We cannot answer your question as we do not have all the facts. Usually any overpayment is recovered in the following months payment.
We would advise you to seek help from your local Welfare Rights Specialist; you can find your local Welfare Rights Organisation to help you with advice by clicking on the link below and putting in your post code, it will then come up with a MAP with a list of agencies in your area
advicelocal.uk Gary