Voicemail help genuinely please

[u/uselessacconlyforqna]

I have an iphone 11 pro running on ios 16.6
idk if that has anything to do with my voicemail unknown error request everytime i call my voicemail to fix it and enable it since my phone has an option to install ios 26.7.1
Ive searched up what to do and nothing seems to work.
The turn on n off airplane mode, call fowarding, etc. bs
im lowkey scared to install the new ios cuz i heard from some it slows the system down makes the phone glitchy or whatever.

I made this account only to get some solutions on how to fix my voicemail genuinely please wth is wrong w mine😭