You can open the gas fill door manualy through the trunk. Pull back the carpet on the right side and look for a small rod to pull. This proceudre is described in your owner's manual.

What country are you in? What year is the car?

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'90 300SE 298k
-300K and it gets put into retirement.
'80 300D 255k Purchased new by family in 1980.

Had a:
1973 220 (gas)
1980 300SD
1992 400E