Want to convert a garage 4 wire receptacle to standard 3 prong receptacle
The NEMA 14 series connectors are the correct, legal, safe and state-of-the-art connectors.  It is absolutely correct for the electrician to install NEMA 14 unless you specified NEMA 6. 

NEMA 10 is obsolete and dangerous, as it does not have a ground wire, and the usual installation process ties neutral to ground, which is asking for trouble. 

You say your plug does have a ground wire, which makes it a NEMA 6.  It is fairly trivial to convert a NEMA 14 receptacle to NEMA 6, since all the needed wires are present.  Or you can change the plug/cord on the appliance, the neutral in NEMA 14 is simply not used. 

You will need to change the breaker to whatever size of NEMA 6 you fit.  


One NEMA 6-15 socket -- 15A breaker
More than one NEMA 6-15 socket -- 15A or 20A breaker
Any number of NEMA 6-20 receptacles -- 20A breaker
NEMA 6-30 receptacle -- 30A breaker 
NEMA 6-50 receptacle -- not allowed on 10 AWG wire