Hi I paid the bill with cash, I thought it was a paypoint and tried to phone them today but they said they dont operate at the post office I was in

Hi, I'm with Scottish Hydro and paid a 230 pound bill i February and have been contacted to say they haven't recieved it. I paid the bill at the post office and unfortunately have lost the reciept. I went into the post office and the woman there searched the records but couldn't find any records of the transaction. Paid the gas bill at the same time and that was recieved so I suggested the woman search for a record of that to see a transaction at the same time but she couldn't find a record of that either. Realize that it was incredibly dumb to lose the reciept but losing 230 pounds seems a large error, can anyone offer any advice?