I am with Virgin Mobile a bit over a year now and this issue has not been solved yet.
When I am on 4G network my phone won't receive calls. Incoming calls go straight to voicemail without my phone ringing.
If I change to 3G or 2G network manually then it receives the calls. I sometimes have to use my phone in this setting otherwise I won't receive calls but then the internet speed goes down dramatically.
I have already tried all the solutions such as manually selecting Virgin 4G network or trying to select another network and switching the phone off and on. Checked EE network and there is no problem reported in my area.
Recently has been sent a new SIM card because apparently I was using an outdated SIM card and the new one came today but still the same problem persists.
I have spoken to customer services and after trying all the possible solutions they think the phone is the problem but I have been with Three for years and used it in the same phone and never had this problem. My phone is OnePlus 3T.
Sort of the last hope I am writing here maybe there is a solution, if not I'd have to switch to another network