Can't check stock room due to 3 people on shift

My husband received 2 nike golf t shirts as gifts. One of which was the incorrect size. We visited the canal walk branch who was willing to change it for a different size without the receipt, however they didn't have it in the same colour.The ladies were nice enough to check which stores had stock. We chose to go to the V&A branch, which is about 30 km away but was the closest. My husband went all the way lastnight only to be told that he can't change it with no slip. When he mentioned that canal walk sent him there, the assistant Pam said she can't go check the stock room as they are short staff, with only 3 assistants. This is totally unacceptable and he is now sitting with a t shirt he can't wear.