Requesting replacement iphone

I just bought new iphone 14 pro max a month ago. On the 2nd day the phone having charging problem (manufacture defect) and i went to apple authorised service centre to get replacement instead they changed the entire part with same screen and back camera. Also there was changes in serial number. As per my understanding, this was not means by replacement. Apple support rep has promised to replace to new phone but end up repaired the old phone. Anyone has faced the same issue as mine?