Let's say I'm driving out in that storm and my car goes off in a ditch and the only tow-truck driver available charges me $1000 for hauling my car out of the ditch. Desparate, and with no other option, I pay it. Does this mean that every time I need a tow, if that same tow-truck driver is the only one around, I'm obligated to pay him $1000 because we, supposedly, now have a contract for that amount?
Well, if you were stupid enough to call him again, I'd say yes. But, in this scenario, the "tow truck driver" pulled you out of the ditch last month for $100... and had pulled you out many times before for a hundred bucks (you sure are a crappy driver!). Then, he called during a storm and said, "I know you have a lot of cars in the ditch. Do you want me to get them out?"
"Sure!" you say.
Then, you call a while later... there are still a lot of cars in the ditch... and say, "Are you going to send me a bill?"
"Yes", the tow truck driver says, and keeps on working.
Finally, you get a bill for $3000 dollars. You assume he's pulled out nearly 30 vehicles and pay him saying, "You need to get me a detailed invoice." The unspoken word here is, "You've done work for us in the past so, we're satisfied. But, we're still going to need the documentation for the auditors."
Later, while work is continuing, you get more bills for $3000 and $4000 and $5000... along with invoices saying the charge is $500 per vehicle, plus a surcharge for tow-strap cleaning, plus $98.50 per hour for 16.5 hours per day for his bookkeeper, even when she's getting her hair done.
You say, "No!" and stop work.
The Judge says, "You agreed to $500 per car when you paid the first bill."
In this case, you didn't "call him again". You just didn't stop him from towing vehicles soon enough.
Further, all along, you say, "We need to talk about this bill." But, the tow truck driver will not talk or change the bill. He goes to court and sues for his money.