Approximately two years ago, a client paid £20k twice for one invoice.
Since then we have phoned and emailed telling them (numerous times) the details of this overpayment. At first we were simply asking them how they want to be repaid as we do not work for them that often , then it became apparent they could not find this duplicate transaction. It has been very difficult to get anyone to respond to us on this.
However, recently, we finally did get a response from them saying there has been no overpayment and it must be an error our end.
The company in question is huge (£600m turnover) so perhaps its understandable that they can lose £20k..! Question is, what do we do now? I am tempted to just write it off as exceptional income otherwise it will just stay on the balance sheet indefinitely.