I filed an amended 2023 return last spring. Months later, the system said a letter had been sent to me, but I never got it. No one at the IRS has info. What to do?

I filed the amended 2023 return in March of 2024, after the initial tax return completed processing. In June, I called the IRS to check the status and was told a determination regarding the refund had been made in May and a letter had been sent, but I had received nothing. The person on the phone said there was some kind of system problem and she couldn't see any information, and I should call back another day. In August - same message from the automated assistance about the determination in May followed by a letter having been sent, same story from the person on the phone about not being able to see any information in the system. In November, the same thing happened, and I got the same story from the person on the phone, and so I asked if I should just re-submit the amended return. The IRS representative said I should do that. First, does this sound like the right thing to do? And second - how would I do that, since the IRS system is telling me the amended return has already been reviewed? Very puzzled - and grateful for any advice you may have!