Go to your local electric supplier, buy a “circuit tracer”, it consist of a transmitter and receiver. Plug the transmitter into the circuit that is cut, at the source,and walk down the feeder until you lose the signal on the receiver. That will tell you approximately where the break is.

Ok…get an electrician or buy (fairly cheap) a tic-tracer..(or similar product).they sell them at Home depot or Lowes… its blue usually…..make sure power is off….hook one end to the tracer….the other is an amplifier similar to what the old time telephone guys used) that beeps as it senses the signal the tic tracer is sending into the wire….the amplifier picks up that signal as you get closer to the wire…

Call him back……….his bad!

You should call an electrician. the contractor is responsible for what he breaks. There are enough advertisements out that tell a person to call before they dig.

Not being able to locate it with a detector may indicate that the line is in PVC or other.
You should be able to determine that by digging at the power supply end and at the barn.
If it is encased in PVC or other, then
you could just pull the wire and measure. Once you know the distance, then uncover the break, and you can re-insert the same wire. Same can be done from the other end. Then splice.

TURN OFF POWER!

the contractor should be responsible for cutting the lines and should be put into their hands to repair the break

hire an underground locating service and a liscensed electrical contractor, and take what they charge out of the money you owe the jerk that broke it.