I sent my CF83 in Jan 2024. In June 2024, they asked for more info as they could not locate me. I sent another letter with the followup information. I got no reply so I phoned them in October 2024. The gentleman explained that there was a backlog and hold tight, but he did try to locate me on the system. He made quite a few attempts and eventually told me I would need to wait for my letter to be dealt with. In February 2025, I phoned again as I had heard nothing, this lady told me to complete a form to retrieve my NI number, as they one was quoting was invalid. I filled out a Form CA5403 and sent it off. In the meantime, I contact my old employee - one of the large UK banks, they confirmed that the NI number I had was my number (I had taken it from old payslips). I have not heard anything on Form CA5403 and phoned HRMC today. The gentleman tried to help but said the issue is that the NI number I am quoting does not exist nor does any recording with my personal details appear on their system, because of this he cannot check the status of either of my requests as they could not be attached to any record. I think I am now at the point of giving up but wondered if anyone here has any wisdom? Many thanks!