Handed over for credit card debt paid in 2013 already.

I have been under administration and my FNB credit card was one of the accounts on the administration list. The full outstanding administration amount was settled in January 2013 already. For 5 years I did not hear any word of any outstanding amounts from any one of those debtors, including FNB. In 2018 a company called Groenewald and Lubbe attorneys contacted me claiming payment on my FNB credit card. Since I went under administration I have never used any credit card again. And I did get an 74 U letter where the court stated that the full outstanding amount was paid off. But it seems that while I was under administration interest was added to the amount on this card - that should have been stopped when the administration order was issued by the court. I did take the matter up with FNB ( I do have all the emails and info sent to and from them) whereafter they requested me to forward the administration and court documents. This was forwarded in September 2018. In October 2018 I made another follow up with FNB... No response. Today another debt collection company Barrett Assc. sent me an SMS demanding payment on my FNB credit card (Reference number FNBL 110157). How can FNB, again, hand me over after not responding or trying to resolve my query on this this account? Can you please investigate?