New SIM card in same phone

Changing sim cards is a fairly easy process. The sim card only holds your phone number's access to the network and none of your information like contacts or apps. Since you are using the same phone all of your stuff will still be there and all you will need to do is restart the phone once the sim is updated and you swap them out. Someone would have to move your phone number from the old sim to the new one and that should be done with a simple phone call to our customer service.

With that said, I am skeptical that the sim is the issue. Usually, if the sim is the issue, you will see loss of signal, sim card errors, or "emergency only". I am curious what troubleshooting you did and what they expert you talked to suggested. Here is a pretty extensive troubleshooting flow for texting issues Messaging and email troubleshooting Some of the steps seem unimportant, but one thing I learned from working in tech support for a while is to avoid skipping steps. Sometimes, a silly little thing happens that cause issues and if you overlook it, you can totally miss the resolution. 

If you have done all of that, then proceed with updating that sim card as an additional troubleshooting step. I just wanted to provide more resources so you can try things before having to call again.