Rental defaulters

The directors of the company rented out my house for a year and a half and missed monthly payments including utility bills until they opted to vacate the house, there have been numerous attempts to get them to settle the outstanding amounts. It's been about 7 months now trying to get them to settle the outstanding but to no avail. The lawyers have tried to serve them with a letter of demand but they do not want to provide a physical address to be able to deliver the letter to them. The directors' names are Mark van Rensburg and Herm**** Fourie.