Mal

I received a cheque for a tax refund, which was a nice surprise, because when I checked my personal tax account, I didn't think I had a refund due. Then checking HMRC letter carefully, I note that the national insurance number is completely different from mine, although all other details e.g. address, are correct. I tried calling HMRC but after 15 mins gave up. Should I bank this cheque or send it back??