InvalidSim card

[Android Central Question]

Hello, I have a Galaxy S6 through Straight Talk. And every couple of months (2-3) I get a message saying that I have an invalid sim card. So, I have to order a new sim card every 2 months. I have to order a new sim card, wait for it to come in the mail, then activate the new sim card. This has happened at least 3 times in the past 2 months. I don't know what is going on with this phone. It is really aggravating though. Does anyone know why this keeps happening? Has this ever happened to anyone else or has had this same problem?