Credit at Jet

Hello Peter Last year I had an outstanding credit of 3000 at jet,I decided to pay every cent in the middle of the year in 2020 around May. Jet at the end of 2020 called me saying I have an outstanding of 1500 And when I asked them to explain how did I get there they dropped the call on me.i would like hellopeter to help me to resolve this cause I can't pay for something I do not know and every time they call me the amount is increasing.