You can achieve some success to unscrew the filter by pushing the front of the lens against a rubber surface (the underside of a mouse pad, or and inner tire tube for instance) and turning the lens.

Don't be too happy to fast, among possible damage:

• Slightly bent lens barrel (no way to align optical elements after that)
• Slightly bent camera body around the mount(*) so all your lenses become misaligned (does the camera still work with other lenses? No loss of sharpness in any area of the picture?)

A service shop should be able to make a first diagnosis to evaluate the real damage.

This said the lens you will get back will never be the same as the lens you loved.

(*) Possible check with a spirit level (the masonry type, that has both horizontal and vertical bubbles), and a L-bracket

• Find a flat and horizontal surface (table top, kitchen counter top, use the spirit level to check)
• Put the camera bottom on it (the lens can extend beyond the edge)
• Put the spirit level in a vertical position across the edges of the front lens, it should be strictly vertical.
• Put the camera on its side (with the L-bracket) and repeat the check (level still vertical, but since the camera is rotated it will check a lateral bend).
• Ideally, do a first measure with a known good lens and camera, so that you can check your measures
• Then check your camera with a good lens (bend in the mount/body)
• Then check your damaged lens (after removing the filter) if there is no visible damage to the front lens rim)

You can also do a similar check with the camera facing upwards, the level is easier to use (just lay it on the lens), but it is somewhat harder to make sure that the camera is strictly horizontal and remains so for the whole measure sequence (requires a very sturdy tripod and head)