iPhone 13 Pro Max repair

Greetings everyone at apple,

On the 8th of August, this past Monday, I sent my iPhone in through the the mail-in repair for an issue that was pertaining to the issue where my iPhone has very frequent no service / cellular signal malfunction. The secondary issue was the cellular internet , the issue is also grandfathered into the cellular no service/signal issue.

Fast forward to August 12th Friday, today, I have received my phone back from the repair center where , upon my knowledge when an issue as mentioned above were to occur, apple would usually replace the entire device under the 1 year limited warranty from the date or purchase/activation. What happened at the repair center, was rather odd. The technician,instead of replacing the entire device , replaced the iPhone 13 pro max rear system , retained the original display? and the original camera module?.

Apple support, I am really confused and I actually feel deceived . I need help to know if this is a correct procedure for apple to repair iPhones . I hope my enquiry can be answered

Best Regards