Primark Refused Exchange Without Receipt Despite Manager Approval

I recently visited the Primark store at Green Acres Valley Stream to exchange a pair of chino boys shorts in size 11–12 for a bigger size. I no longer had the receipt, but I had paid by card and only wanted an even exchange, not a refund. In the store I explained the situation clearly to several staff members, including a manager. The manager told me that I could do an even exchange, but when I went to the register the exchange was still refused. The staff at the register were very rude to me during this process, which left me highly upset and disappointed with the way I was treated. This is the first time I have experienced such an issue at Primark, and I find it very frustrating that I was given approval by a manager for an even exchange but then refused at the till. I request that you allow me to exchange these boys chino shorts for the correct bigger size as originally promised in the store, and that you address the behaviour of the staff involved so that other customers do not have a similar experience.