How did you imagine you would receive the call statistics in that scenario?

This sounds like you lied in the interview to get the job, but reality has hit you. Sink or swim, good luck!

Had this problem with Verizon, after MONTHS of inconsistent calling we were able to pin it down to their phased implementation of STIR/SHAKEN and how our calls were presented to them. We had to make some tweaks, and everything went back to normal. Make sure either the FROM, PAID, or CONTACT headers have the IP address of your billed trunkgroup IP address, or add a diverted header to the call from the SBC. Good luck!!

Use a session border controller to manage your NAT’ing