Got a complaint by a customer and this guy is a complete t

t.
his neighbour said he was like this.. he was supposed to tell them i was coming so i could use there land to work from doing some of it. They were in, and he didn't tell them - they didn;t answer the door so i just went on and did it - they saw me and was like wtf are you doing???

Managed to sweet talk them around, and they said he is a complete idiot.
He lied to my missues who took the call today! and its been over 48 hours since i did them by saying he wasn;t there when i cleaned them, in order to inspect them. Funny, he was in his kitchen and gave me a cheque when i finished

Moaned about them not being done properly, and was very rude about it. Now i took over an hour (he said i was only there for 25 mins).
Went round to see him and the windows an hour after he called, for no one to be in, apart from his dog, so i made the dog bark for 5 mins to ensure he knew someone was at the door - and his neighbour the other side came to check what was up.. and left a note saying the time/date/day and a short message saying i will call back tues morn. (Im very willing to assist on any complaints!)
Alsoim very willing to just drop him and refund rather than pee about with this guy. I wasn't planning on going back very soon anyway.
Now ive already put his cheque to the bank, so apart from him cancelling the cheque, how long legally do i stand before i have to pay his money back to him.
I dont want to pay him back in cash for him to cancel the cheque, and them im a further £££ out of pocket.
I was gonna give it 28 working days before i refund his money if he is not willing to stop the cheque. Can i legally do this? what is the best way to do this?
Suppose i could phone the FWC on Monday to find out.. make some use of them.
what do or would you do?