Speedometer in CVR 2008 moving while car is stationary and also D blinking

Hi there, my car is Honda CRV 2008 , i take it to garage last month for a repair of crankshaft oil seal which was leaking. they told me they have to put down engine and gearbox and insert the seal, after that they put back engine and gearbox, and there problem started, first the car wont start at all, then they saw some ground wire going to starter motor was not connected, then after connecting it it start, but with bizarre results, D light is blinking even if gear selector is at P position, also speedometer is moving while the car is stationary and when you select D speedometer goes back to zero as normal. on driving it can not reach 3rd gear and no speed at all. Engine Light (Check engine is also one and after reading code on OBD 2 it shows error code as U0122.
Please help as i don't know what to do and the mechanics seems is out of alternatives.