Unfair Treatment & Service From FNB

I had a revolving loan with FNB, they handed me over to Groenewald Lubbe Legal, in 2019, I got a settlement letter & paid the debt on the 2019 - 08 - 16, until today I am still getting calls & messages from Groenewald Lubbe Legal( Debt collectors for FNB) that I am still owing, I have a POP & a settlement letter, moreover, I am still listed with with the national credit which when the collectors calls me now the amount has increased even to 8K, in 2019 I paid R7365 which was the settlement amount needed. they got their money but I really don't know what they looking for, they are not even clearing my name from the debt reviews, so I am even struggling with my credit ratings. May someone please help me with FNB & Groenewald Lubbe Legal