FIRST: You need to find out what's in the tank.
See if you can drain fuel by disconnecting the line that feeds the pump (at pump) into a clean container and inspect. If not, siphon it out the tanks fill tube.
You may be the victim of vandalism, as your car was fine before. Tanks don't "rust up" during 'normal' operation(s).
The pumps at Stations/Markets have filters so debris can't come through, just water which will kill the engine right away. This rarely happens with the modern (EPA approved) dispensing equipment.
It's a "process of elimination" is all.
Good luck.
