UNABLE TO ACTIVATE.

I can use an iphone and I am pretty knowledgeable in regards to resources like the internet. So that being said I have tried everything. I truly dont understand what happened to my phone it will not allow to connect to my cellular provider. It showed me again and again cannot connect to cellular provider, update is required then I finally perfomed the update which it would not allow me to do on my phone I had to connect it to my macbook and enter into a recovery mode to force it to update and after it updated still no cell phone coverage so I went to my provider they gave me another sim card nothing. I then factory data reset my phone which was an even worse option because now it won't let me activate it at all and I cant use my phone what so ever. I have the 12 pro max ive probably had it for 4 months and this all happened unexpectedly after the software update. please someone help me I am desperate