Pathetic and shady practices

Worst accounts department ever, they never send you a statement, every month you fee for the un capped adsl is a different amount, in april we owed them, according to their system R1000, we paid R1600 and told them to cancel the service, now all of a sudden we owe them R2000, we have not had internet or a functional line since april, where does the R2000 come from ?