Happened to us. A family member called up the neighbors' oil company to 1) let them know that they filled the wrong tank so our neighbors did not run dry and 2) to settle up with them for the oil that we'd use anyway.

The guy on the other end immediately got mean and aggressive with my family member and went right to battle mode demanding full payment. They got a call back a few minutes later letting them know they could eat a bag of dicks for talking to a nice lady like that.

Never did get a bill for the mis-delivered oil.