Yes, I have on behalf of my mother. She had a letter from ProSearch who wanted to verify that my father had used an address which was in their records. I phoned them and because we had no idea that he'd used that address, they said they could go no further. I phoned the parent company Equiniti and was immediately told what it was about, apparently some shares that my father had bought years ago and about which my mother knew nothing. They sent a form to fill in, which we did, and we then had a letter wanting confirmation of the aforesaid address, which we hadn't got. Phoned again and was told to just send in a letter confirming the address, which we did. That apparently was enough as they started sending cheques and a letter confirming that the shares had been put into my mother's name. No mention of a utility bill.
Equiniti act for companies who have shareholders they can't contact. It's worth pursuing imo.
Good luck.