How to loosen tight valve cap on bike?

This is just a regular bike I use for riding around town. I get on it and ride it; I don't know much technical stuff. Anyway, my bike had a flat tire last year. I took it to a shop to be fixed, then didn't have to add any air till winter came and I put the bike away. It's good enough outside to go biking again but now I need to add air to the tire. Well, the valve cap is incredibly tight! I simply could not get it off the tire. I struggled with it for half an hour just now and could not move it. I tried using pliers, I wore gloves for more traction, and nothing worked. It would not budge. It's like the shop superglued the stupid thing back on when they fixed the tire. How can I get the valve cap off so I can inflate my tire?

P.S. Please don't suggest taking the bike apart in any way. I don't know what I'm doing and if I start taking apart pieces, I don't think I could get them back on safely. I'd really like a simple solution that I can complete at home, if at all possible.

At this point, you may have a safety issue. Valve stems weren't designed to be torqued with pliers. Take it back to the shop that put the cap on, they should remove it and check your stem with no charge. Expect to pay for a new tube if it is damaged.
You do know to turn that counter-clockwise when it is at the bottom or clockwise if at the top?

Turn the wheel so the valve is at the top. Spray the area between cap and valve with WD40. Gently grip the cap with pliers and wiggle it back and forth until it unscrews. Be very careful not to tear the valve.

Use a Exacto blade, cutters or heavy scissors to cut the cap part way off. You should be able to use a small screw driver or other tool to pry the rest off.