Two complaints I see about gas stations..
This is one (The hold) I suspect you used the TRUCK lanes to fuel up
The other is the 50/70/100 dollar limit at some pumps
Here is what happens when you swipe your card at the pump....
The Pump requests a hold on the card for whatever the pump limit is
Then you pump. and when you hang up the nozzle the pump is supposed to send the amount you pumped and request the rest of the hold be released.
Some card companies are slow to release the hold
And occasionally there is a "Glitch" when the pump goes to "Finalize" and it takes a day or 2 for someone to process by hand. 
The reason I suspecdt you used the truck lanes is the 500 hold. In the auto lanes or RV lanes it would more likely be 100 or less.