Amusingly, telcos do this to each other too. I worked for a back haul carrier and AT&T would send us a literal truckload of paper bills every month that looked

Amusingly, telcos do this to each other too. I worked for a back haul carrier and AT&T would send us a literal truckload of paper bills every month that looked just like your standard phone bill for calls that we terminated on their network. They consistently net over-billed by about 10%. So of course we had a data entry team whose job it was to enter every claimed AT&T charge into our system so we could then reconcile those with our Call Detail Records and dispute the overage.