Most photographers likely had to deal with this at some point.  Stuck polarizer filters.  Internet is full of advises, including many YouTube videos.  As dominantly nature photographer I also had to deal with it several times and was able to unscrew it using one of these methods.   Until only inner ring got stuck - not entire filter


[Inner Polarizer Ring stuck on top of Camera Lens]


[Polarizer Filter left and inner Ring right]

Anything I tried didn't work.  It was stuck good.   Even apparently bulletproof method when everything else fails - hose clamp - didn't help;  just couldn't get enough grip


[Hose Clamp - photo for illustration.  If you try this one use rubber gloves for grip and separate lens from camera first]

Next step - took it to several camera stores that had repair shops.  At one place they had special machine that is used for cases like this.   Tried - no success.  Rest wouldn't even touch it afraid not to damage the lens; gave me advises instead of which I was already aware of.     I was ready to give up.   Then one afternoon I met photographer on photo shoot in local park.  I chatted with him and he told me he had same problem and was able to fix it very quickly!  How?  Pliers. Believe or not.   Grab and squeeze ring, then twist it couple of times.  I didn't think it would work, but I gave it a try.  Instead of pliers I used adjustable wrench


[Adjustable Wrench I used instead of Pliers]


[Get a good hold, then twist off at couple of places (This shot was taken later after ring was already off, you can see on top where I was able to rip it)]


[Within 10 seconds ring came off!]

You need to be careful not to damage the lens - always take lens off camera first (photos above are for illustration).  Sending lens to Canon would solve the problem;  they would saw it off, but would charge you dearly.  DIY is always the best option if possible.

 
Hopefully this can help someone.

Recently image rejected couple of times as RF for following reason:

Metadata - Commercial Requirements: Contextual metadata such as titles, descriptions, keywords, categories, and locations must be accurate, descriptive, and relevant to the subject matter and must be in English. They should not contain any potentially objectionable or offensive language, as well as any trademark issues (brand/company name) or sensitive information. Please remove special characters or repetitive words/phrases and check spelling/grammar errors.

Image is attached.  It's not what's in the image, it's metadata

Title

Famous Olympic Games Stadium Exterior on Montjuic Hill in Barcelona, Spain also Football Club Sports Arena Venue

Keywords:

amphitheater, architecture, arena, barcelona, blue, building, catalan, catalonia, championship, city, classical, culture, day, europe, european, exterior, facade, famous, football, historic, landmark, mansion, modern, montjuic, olympic, olympics, outside, park, popular, sky, skyline, soccer, spain, spanish, sport, sports, stadium, sunny, theater, theatre, travel, urban, venue, wall

For the life of it I can't find the problem keyword. Can you? Only one I can think of is "olympic".

Recently I spent 6 weeks trekking in Spain, last 2 on Canary Islands.  Had a chance to visit spectacular place - Roque de los Muchachos Astrophysics Laboratory on La Palma.  Nearby is "Monumento al Infinito" or Monument to Infinity -- more details https://www.starsislandlapalma.es/en/walking-and-observing/astronomical-viewpoint/monument-to-infinity-astronomical-viewpoint   

It is a spectacular place, and virtually no offering on stock agencies, so I took couple of shots.  Uploaded 2 - horizontal and vertical - as non-editorial to Adobe.   Vertical gets accepted


and horizontal rejected for "Intellectual property Refusal" reasons


After uploading as Editorial it goes through.  So now there are 2 images of same place, one as Editorial one as Non-Editorial.

To make things even more ridiculous,  on Shutterstock  Horizontal (Editorial on Adobe) is accepted as RF, and Vertical (Non-Editorial on Adobe) rejected as RF, and accepted as Editorial.   
----------------------------

Can anyone comment, should these be Editorial or non-Editorial images?   Judging on above, I don't think Reviewers really know and it depends who you run into