I have tried to cancel an order for helium cylinder because I didn't read it details properly that you had to collect from seller. I am unable to do so. I have messaged the seller twice and they are not getting back to me
Buyers can request cancellation but sellers still have to implement it. If you can't collect they will have to cancel and refund your money. If they don't refund open a "not received" case on ebay within 30 days.