BT Mobile & iPhone 14 - calls going to voicemail too quickly - how increase rings?

[Wargravian]

Hi, I’ve got an iPhone which I use with BT Mobile. When I get an incoming call, the phone only rings twice before the call goes to voicemail (or a missed call). I would like to increase this to at least 10 seconds to give a sporting chance of picking up. By the way, this is nothing to do with “do not disturb” or similar fancy stuff. Can anyone help please?

[rbz5416]

If you Google or search these forums, this seems to be one of those questions with no definitive answer. Some say it's fixed at 20s, some say it can be increased to 20s & others reckon it can be changed  by putting the SIM in an older phone. Absolutely no idea how that could work.

If you have access to another phone I'd try the SIM in that first, just prove whether it's the phone or SIM.

If it proves to be the SIM then you'll have to work through the options others have posted & see what happens.