Not at all on digging up the tank.

And a signal float is intended for a control panel where it sends signal to a relay etc for a control panel. Not enough juice to run a pump... CV byBut if you just tell them you need a float switch, that's what you're going to get. You need to tell them you need a wide angle pump rated float or an operating switch.

Yep get a new pump and operating float (make sure it's not a signal float - pump rated for amperage equal or in excess of the pump's FLA). Pull it out, plumb the new pump in with your ball valve check valve union as they presumably did there. Probably need some pipe a few male adapters some primer glue etc. You'll see what components you need. It's tough to plumb out of the hole usually you evacuate the tank then plumb so it all fits but still can be done. Make sure your check valve is on the discharge line below the ball valve so you can isolate it. Check valve is a must make sure it opens with the discharge flow not backwards.

Likely a break in the main.