Pathetic

I am getting emails stating I am owing this company R622, but I'm getting emails every day and every second the amount owing is more and more, I have no business with this company and according to them I app**** in 2015, They email me, no phone calls.. Oh and threatening sms's as well. I really don't know what to do but I am not going to pay them because I do not owe them, how can they contact me after 3 years to let me know of an outstanding balance owing