Dosen't help the OP but I had similar issues on 4G and that's what I originally thought but I ran cell info on 2 phones with both EE and VM sims, (both sims in each phone) and the Virgin sims were connecting to the same EE tower, but just with lower signal strength. Same phones remember, so not hardware related at all.
That added to dropped incoming calls and constant distortion that basically sounded like low bit rate, I gave up and have switched back to EE. Plus I got WiFi calling back 🙂
Things might be better with a 5G phone, I didn't have access to one at the time.