Mom put $300 as a deposit on a retirement apartment but moved in elsewhere, and now getting run around getting her deposit back. What can we do?

She put the $ down, end of May, and has made numerous calls to two staff, and yesterday, the executive director..."we sent it 2 weeks ago...call the Post office...and lying about Mom's calls, as if she doesn't remember the prior conversations....The site is Waltonwood, Lakeside, Sterling Hts., MI, and I know that Singh company runs it...do you know an address for Singh to submit these complaints and get her $300 deposit back, which they said would not be a problem if she decided to move in elsewhere, which she did. Thanks! My Mom was so stressed yesterday, and she said she argued with them for 20 min., then they ended the conversation by saying, check the post office...must be there, then they hung up. This is unacceptable and I want to keep pursuing the matter!!