Bad situation. If you have that techs phone number, then you can get his address, drive to him and demand the control back.
Next, you say you can't use the RV. Jacks are down? A good tech would be able to hot wire the retract valve. Or, crack open a pipe and allow the ATF to drain.
Finally, when you do get the control back, a good electronics tech (TV repair shop) should be able to ascertain whether the device is repairable. You could also take it to a local college with an electronics program and have the 2nd year class work on it.