How do they work out the end of UC claim due to change of circumstances?

I was claiming UC and received a small inheritance which took me over the £16,000 limit which I declared.

I should have received the inheritance on the 18th June but my sister in error put it in my son's account. On the 20th June I managed to get part of the money and the remainder on the 24th June. On the 24th June I used my journal to declare the inheritance and that it should have arrived on the 18th June but there had been problems. I had an appointment at the jobcentre to discuss on Saturday 28th June. They didn't know whether to close the claim and sent it to a decision maker. I then chased this after 2 weeks.
I then received a letter dated 16th July closing my claim on the 18th June.

Today I received a text asking me to check my UC journal which was impossible as it was a closed claim. I rang the helpline number and they read out a letter saying I had been overpaid by £1700 approx and the date of the closure was 24th May because I was late declaring the change of circumstances. I was expecting to repay from the 18th to 23rd of June. The delay was less than a week and could not have been on the day because I did not get the money then because of the error.

The UC,PIP, JSA and ESA (Claims and Payments)Regulations 2013 , part 3, Reg 37m (3) says that you have a month to give information.

Can I be asked to repay nearly a month of money because I did not declare on the day the inheritance should have arrived?