Cupalskii

Hello, so I have been sent a letter from HMRC about the self assessment but it’s for my dad that passed away last year, the letter says I was his personal representative to which I didn’t not agree and also was not in contact with him at all. I can’t get through to HMRC as they are “busy” as well as it states I have to pay 7k which I don’t even have that much money nor would I be able to pay that in that amount. Could someone help me with this as I feel like my name was used illegally for this matter. Thanks