Ihs property management - bullies

I received a letter of demand today the 10th February 2023 while I moved out in December 2016 and do not owe them anything, in fact I did not even claim my deposit back. When I called to enquire they told me they can't check their system as to why I received the letter that threatens to blacklist me if I don't pay them R5500. This is so unprofessional and unnecessary really. I better get ready to engage my lawyer because I refuse to be blacklisted because of their unprofessionalism and greediness.