Adding A Garage to a Legal Non-conforming property

[Viko Henna]

We want to add a garage to a 4plex but the city has re-zoned the lot to SFR use and says our property is legal non conforming so we are not able to expand.

i think a garage is an accessory that is consistent with accessory's for a house,  so it should be OK to my thinking, 

Is there a tact full way to approach the city with this?