marjan, do you have the tow company's phone number? if so, use it!
sounds like you all need to get vocal as a group-the residents-to get this ironed out with prop.mgt. i know it must be frustrating. do your spaces have apt. numbers painted on the spaces? that doesn't always work but it may be a deterent. also a monthly newsletter to advise other tenants to advise their guests where to park?
unfortunately ppl will be ppl and many are not caring about being considerate and others just don't notice things unless it's pretty obvious.
hope you all can get this resolved, but i think as a group your voice may be heard more clearly.
oops..also try to restrain from anymore keying...