Paid out loan but keep getting messages to pag

I recently settled my loan with direct axis,which I had asked for a settlement letter then paid the amount that was on the settlement letter, then emailed them the proof of payment as requested by them,now they keep sending me SMSs of an outstanding 3500 which I don't know what it's for! These people are a pain and abusing their consumers, I thought I was done with them and their bad service after I settled the loan but it looks like they want to carry on abusing me please help me!!!