I have a law question..can an ex employee do this?

i worked parttime at a company..in which were family friends!we got into a personal dispute in which resulted in my quiting!they tried to call a few times and i let it go to voicemail..they still owed me money for a job.and i still had a key! Just 6 days after my last job they had the locks changed and sent me a partial check charging me for the locks! $122 bux.and let me know i was terminated!the reason i ask is i was told they can not do that unless they gave me some written notice of a time line to return the key!or was is my application or any agreement at all!also i have known this family for 12 yrs i called the lady mom!they absolutely knew i would never ever do anything to there property!this is out of spite i do believe!what do u think..or should i have a civil suit and make them pay me and allll court costs!i have plenty of time =]