Ok, so after the site meeting they left monitoring equipment attached to the line in order to test the link. The link tested fine from the exchange, they just re-testing from my side to prove to me that the link is stable.
I know the link is stable because it's only 1 call at a time that's dropped (not all at once).
What kind of troubleshooting can I do n my side?
This doesn't happen with internal calls, and the PRI card has been replaced.