2001 Triton stuck in wheel lock

I bought a 2001 Triton 2 days ago and new to 4x4. I drove it straight to mechanic for a service because it was sitting around for nearly a year. When driving it home I saw the wheel lock light on. And since then I can’t get it off.

I reversed up hill out of our driveway and there was a huge clunking sound near the rear, and the rear wheels did a shuddery skidding action. Now not sure what to do now. Light remained on while driving all day. Not game to reverse again!

Note I never entered 4wd it was on in 2wd when I picked it up from service, and light wasn’t on when I bought it.

This Ute has auto lock, but I was wondering can you manually unlock them? Or is something else going on? Maybe it’s really still in 4wd?