Pay dates

My partner joined UO on the 22/6/25 and the pay date was at the end of June so he missed out on that which is fine due to cut off dates etc for new starters. However pay day for July came yesterday after working 80 contracted hours over the month of July plus 20 in the week he started plus overtime and was paid £260 and told he won’t get anything until the 28th August. Someone please advise as this is not correct. I have been a Store Manager for 19 years in a different business but I know it isn’t correct but don’t know how to go about it. 🙏 you don’t work 9 weeks before a full months pay surely?