I think these people are talking me for a ride

In 2014 basically lost everything due to my financial position being so poor. I could not afford to pay my accounts at fnb. From then groenewald and lubbe contact me and we agree to make a Payment of R50 per month for the credit card I owed and R50 overdraft I owned and R50 for the smart device I owed. To this date I have been paying them every month on time and never missed a payment. Today I receive a letter of demand to pay the full amount in 10 days or get a debt conciler or face legal action. I think I'm ready to cut ties with these people. I'm sure the my debt should have been prescribed by now as Fnb weren't the ones simmoning me with legal action. Instead sold the debt to these guys and now wanting to get the full amount out of me. To which I can't afford. How do u go about finding out if me debt has been prescribed, because on my Itc report I don't see Fnb anywhere on it. Could someone advice me what to do.