IPhone 6+ won't access cellular data?

So I know all the usual fixes for this, but not of that helps. It's a SIM issue because my old phone had this same problem. A while back, I found a fix involving some sort of APN settings download, but that was a WHILE ago. Was wondering if anyone else had this link or have heard of this issue and know where to find a fix.

Again, I'm well aware of the gazillion articles telling me to restart my phone or toggle airplane mode. That's not going to do anything. This is more advanced than that somehow and requires an actually downloadable patch which I haven't seen in about two years. If anyone has that information, it's greatly appreciated.

You need to go to a store for your cellular company and they will initialize a new sim card for free.