can a text message be legally binding

Text messages are very problematic.  The short answer is that it is difficult to authenicate the text message and thus difficult to have it admitted as evidence in a trial.  The issue becomes that you received actual notice and you may have taken action based on that notice which could be admitted more easily and create evidence of your actual notice.  Sorry for the confusing answer.  But, this is an emerging area of law and not well settled.  Landlords are held to a strict standard when it comes to security deposits.  If you have any question that your security deposit is being wrongfully withheld you should consult an attorney.