If you mean the 2 or 4 prong tool, make sure it's retained with a QR skewer or axle nut.
You need more force to remove. Simple. Bigger wrench or piece of pipe added for leverage.
You have a FREE WHEEL, not a cassette.
It simply screws on and then gets super tightened by simply pedaling.
Add years of not being removed, it may likely have corrosion wanting to bond the parts together.
You might try applying some Penetrating Oil. (WD-40 is ineffective. Get the "real" stuff) and letting soak for a few hours and hope some wicks in.
These OFTEN break the tool when removing.