Settled account but get handed over

Pathcare has handed me over for collections over and account I have settled in 2011 already. I have told these collectors that I will pay again because I have payed the account already. they now want me to send proof of payment to them. this is 2014, where will I get proof of payment that I made in 2011? why are they only contacting me now after 3 years? they claim they have been traying to contact me with no luck, how did they manage to find me now? please sort out your payment tracking system as I have paid this account a long time ago.<br> Setjhaba Godfrey Thaele<br> ID number ***<br>