When a phone connects to a cell tower it does so through software called Access Point Name (APN). This is specific to your provider and identifies your provider, your plan and you. Using Telstra as an example, Telstra has a number of APNs for Telstra, Belong, Aldi, etc. When updates occur sometimes the update includes the wrong APN. Your goal is to find the right one. On your phone you can search the web using the abbreviation Telstra APN but in your phone settings you have to search for the full phrase Access Point Name. Write down separately on paper your phone APN settings 100% correctly. in case you want to revert. Now go to Community page top right, and search for "APN". Go through the various posts there to find one that describes in detail how to update your phone.
The APN is only for internet/packet network..... The "normal phone service" should still work without the APN settings... A call to customer service for your carrier and they can usually push the settings out to your handset
