I find in many cases the retailers are reluctant to offer receipts especially with touch transactions and, you are asked if you want one, as opposed to it being being automatically handed.
This happened to me a while ago in a supermarket (with a non-contactless card). I asked to see the manager and showed him the double transaction on my online banking app). He initially demanded that I give him printouts of my bank statement which I refused to do. After some raised voices he gave in and the refund was processed immediately.
I find in many cases the retailers are reluctant to offer receipts especially with touch transactions and, you are asked if you want one, as opposed to it being being automatically handed.