please advise, overcharge of £135

FunnySaving

In fairness, you didn't notice either and it's more likely that you would have been aware that there was a discrepancy, so I think it's a little unfair to lay all the blame at the cashier's door. Plus there's not a system on earth that will completely eradicate human error, so as long as they are prepared to admit it when it happens that's certainly something. I appreciate that your anxiety made this into a very stressful situation for you, but it has been resolved satisfactorily and no harm was done (apart from your missing night's sleep!) so perhaps chalk this one up to experience and check everything before you leave the store next time.