Help getting refund from smiths reqd

[Kiddy12]

i was in smyths toy shop on Saturday and there was a 3 for 2 offer on Pokemon however it turned out the toys we wanted weren't part of this offfer so we put 2 back and bought 1.However it turns out we were charged for 2 the guy removed the one we wanted and left the 2 we put back on. Phoned store and told them about this gave them all the details and the manager said he'd check cctv but that we'd have to go into store to get refund.the store is 30 miles away so I'd like to know where I stand as regards gettin a refund without going in store?