Missed rent payments, haven't increased rent paid

Since a new tenant moved into our let townhouse, managed by Ryneveld Rentals, the rental amount was supposed to go up. However, they continued paying the old rental amount for the first few months, then stopped paying at all. After numerous emails I did get one payment through one month, but not again. Now we have 3 months missed payments out of 7.<br> No answer to emails, phone calls, mobile number voicemail box is full.<br> Cannot contact them.<br> They've made off with R19000 of my money.