Fuel cap cover

I am no freezing cold expert...
but I speculate the issue is ice build-up.
Either the door is frozen shut to the body or the cable mechanism is frozen tight.
Preventively, I would lubricate the latch and cable (oil and/or grease) in an attempt to prevent water intrusion into the cable or ice build-up on the latch release mechanisms.
If the door is not opening, and you can hear the latch mechanism releasing, try pouring hot water over the door, to break the ice build-up seal.
Good luck.

 

This is one of the VERY limited situations where spraying the mechanism with original WD 40 might be a good idea.
It never dries completely and should help prevent water from accumulating around the moving parts.

 

Careful with that, may “stress” paint. A cup of tea purchased from gas station store and allowed would be short of boiling point and thus safer. Hair dryer or heat gun safer, but obviously not an option at gas station. Mini torch, not held too close?

 

I found those situations especially annoying in my Gen 1, where the filler door was on the right rear quarter, about as far as possible from the release lever by the driver's door.

The procedure I developed was to reach into my wallet and take out a plastic card. Possibly a credit card, or something of lower value, like a library card or membership card for some organizations, as long as it's the same kind of springy plastic card.

I would walk around to the filler door, bend the card a little and shove it in the gap around one of the filler door corners. Then I would walk back to the driver's door and pull the release lever. At the sound of the card dropping on the pavement, I would walk back around, pick up the card, put it back in my wallet, and fill the tank.