Does the Blackview A7 Pro support calls over 4G/LTE? I realise the "local" mast (not very my nearest mast is 13 miles away!) also has to support it as well as your handset. The problem I've got here is using my Three SIM (Three has no 2G fallback) when attempting to make a call it stalls for ages trying to find and drop down to a 3G signal, which is usually very weak, or non-existent at all sometimes. I seem to have a stronger Three 4G signal than 3G, probably because of the different frequency. Three here is very unreliable to say the least. My other O2 SIM works alright, but it would do it can revert to 900MHz 2G.

Unfortunately the A7 Pro doesn't support VoLTE.