Edit: I just saw your edit. Great job fixing it! God I hate that you had to do this.
What is the make and model of the wheelchair and the wheels?
Links to their official website would be helpful.
Did your wheelchair come with a regular manual? A link to a PDF would also help.
If you want to go down a more…questionable route, you could call the wheelchair provider number. Use social engineering by saying you’re from a doctor’s office and you can’t get the wheels to activate.
It helps to have a friend do this for you. You want a buffer and you want your friend to say “I am not sure” or “I don’t know” a lot. That way the company gives him or her more information on what to do next before calling you back.
This is a terrible situation. Maybe your insurance will spring for the cost. It’s so infuriating that if I had access, I probably wouldn’t sleep until I figured it out and posted it everywhere.