My tenants vacated the property on 7/31. we did a walk through that weekend w/ them. I returned their security deposit less $110 less their deposit b/c they bounced a check and had a late fee (stated in lease). I mailed the check on 8/28- regular mail. They contact me 9/11 b/c it was never received and stated we did not have a right to hold any of it and that we owe them double. I calmly responded thatnk you for letting me know. I will stop the checks and drop a new one in the mail (did on 9/16). they told me they will not accept any less then the whole amount and will get back to me about owing them double. I feel extorted by my tenant ( a law student). What should I do?