I got an $1100 past due bill from Kubota once, I realized that was oddly similar to the rental price of the skidsteer I had as a loaner so I called to let them know I wasn't planning to pay it, apparently it was the first time it's ever happened, Kubota gave me a loaner while my machine was in the shop, Kubota corporate is supposed to treat it as a rental, and reimburse the dealership, the dealer sent Kubota another bill and somehow it got forwarded to me, no big deal, one phone call and we were good
I've had other times, I hadn't been paid for the job yet and so I didn't have the cash with me to pay the crane, I could use card but his card reader wasn't working, no big deal, I call the next morning and tell the the office guy "Hey, I have a bill for ~$1200 that I need to pay" and he said "What bill? you don't owe anything" so I had to go back and forth for a little while to get him to take my money
computers and humans both mess up, best bet is to keep track of bills or invoices yourself, that way it would atleast take you, and the other side of the deal forgetting or messing numbers up