If your desoldering pump doesn't remove all the solder and you're having trouble heating the joint, apply some more solder and try again.

If you're still having trouble melting the solder, apply some low‑temp solder to the joint to keep it liquid for longer.

Clean your soldering iron before use to avoid brittle joints from mixing low‑temp solder with standard solder.

Are you desoldering a lot of pins? Or do you just desolder a lot? A dedicated desoldering station or gun is a worthwhile investment.