Hospital asking for repayment of overpaid salary

I am the unfortunate recipient of a letter asking for ~£2000 worth of overpaid wages from August to November at my current hospital trust as they thought I was working more hours than I was. From what I can gather my work schedule and rota were not aligned.

They are asking for full payment within 7 days. They have also said I could pay back from my future salary as an alternative.

Has anyone else been in this situation? What are my rights with paying this back? Am I within my rights to ask them not to deduct anything and for me to pay at a rate that I am comfortable with?

Given that they were the ones that made the mistake and issued me a work schedule and that is a contract of employment do I have to pay them back at all?

Many thanks in advance