Problem with 3G connection

Have you contacted your 3G cellular provider to verify that this issue is not on their side to be resolved and not due to the phone upgrade? Most major cellular providers are in-process of phasing-out 3G service within the next year or two. Yours may be one of them. If this is the case, you would need a phone that support LTE (aka, 4G). Your iPhone 11 certainly does!

You're very welcome! Let us know if contacting your provider does not resolve the issue and you need additional assistance.

Excellent! Sorry, you had to go through the trouble, but I'm glad you got it worked out.