There is this [LIST] Carriers that work or do not work with /e/OS country-wise. You might share the name of your carrier in case there are others who have had particular experiences with that carrier. If you have a carrier who likes to charge a premium rate for support I can understand this discouraging.
I get free support and have found the call handlers helpful in answering specific questions as your first post. They prefer to keep customer’s income if the SIM service is not up to expectation after all.
Re debugging there are some secret codes in the dialer which may be illuminating. You may find better guides or someone else might chip in with what you need but this is what I am talking about: