You can't push the slide stop down to release it? Is that what's happening.
It's designed to be very difficult to drop the slide with an empty mag in place. Put a round in it and it should release normally.
When removing the slide stop pin, I generally get it lined up and then tap it with a plastic faced hammer.
Usually one tap just to pop it loose and it will remove easily after that.
Give this a whirl and report back.
In Memory of Paul "Dietrich" Stines.
Dad: Say something nice to your cousin Shirley
Dietrich: For a fat girl you sure don't sweat much.
Cue sound of Head slap.
RIP Muggsy & TMan
"If you are a warrior legally authorized to carry a weapon and you step outside without that weapon, then you become a sheep, pretending that JOCKO will not come today."