Very unprofessional and greedy

I bought a house in Pelican Park 2015, I was paying the occupational rent before the bond registration in 2018 I received a letter from Marais Muller Hendricks attorneys saying I owe R19 000 of occupational rent when I told them to check their 2015 files they said they don't have those files anymore so there is no proof that I was paying. When I wanted to settle that debt, the settlement amount was higher that the amount they sent on the statement