iphone cellular network disabled on multiple phones that have been replaced on one phone number

I am experiencing the same issue with multiple new iPhones on a specific phone number on my business line. The phones stop being able to use cellular network after a few months of use. I have taken the phones into US Cellular and they were unable to figure out what was happening. They sent me to Apple and they were also unable to figure it out and sent me a replacement phone.

On iPhone #2 it worked well until 3 months in and then the same thing, stopped working on the cellular network and can only use it with wifi. So...back into the store. I asked alot of questions, can the number be hacked/highjacked and another phone is using my cellular data? They told me its not possible for an iPhone to be taken over remotely. Can an app the user downloaded do this to the phone? She said its possible but then described that the app will take over doing things on the phone and change settings, get credit card info, etc. BUT, none of that is happening to these phones. They simply stop being able to use cellular data and can only look at the internet or send texts when on wifi. Huge issue as my employee works out in the forest and cannot access wifi until he gets home or back into town.

Apple has now sent me 3 new phones and they all keep failing like this after a few months of use. So, I'm left thinking it cannot be the phones, it has to be someone hacking them or the cellular system.

I have had all phones current on updates, reset all the phones to factory settings when they started having the problem, checked that the cellular data is on, restarted, new SIM card, etc. None of these things have fixed the problem. On my last trip into the store I asked them to turn the phone line off and we started over with a new iphone and new phone number. I have not had any issues (yet) with the newest phone but wanted to put this question out there to see if anyone else has experienced this? It's been very frustrating since no one at the cell store or Apple can figure out what is happening.