calling my mum's iphone goes straight to voicemail every time

quickest test: ask someone else to call her. if their call rings through and yours doesn't, it's something about your number on her phone (blocked, silenced, saved wrong). if everyone goes straight to voicemail it's a setting on her phone or her carrier. if it's everyone, check whether wifi calling is on, especially if her signal at home is bad.

Going straight to voicemail every time, without ringing, is nearly always something on her phone and not the network. Things to check on her iPhone: - a Focus or Do Not Disturb left on (look for the moon icon) - Settings > Phone > Silence Unknown Callers, which sends anyone who isn't saved in her contacts to voicemail - your number accidentally ended up in Blocked Contacts - call forwarding switched on The unknown callers setting catches a lot of people when the number is saved slightly wrong.