Network issue

I would call this a major issue, IOS 18 has effected phone network connectivity and communication after resting network settings as well as cellar settings, IOS 18 is unable to Make the connection, either software or framework issue, phone network I am with report no issues so apple have somehow made an error in there coding, As have been unable to send text messages and make phone calls correctly showing message failure and dodgy cellur connection, Is apple or a member of the community able to advice on this? Any further support or information? As it is a heart component of the Iphone