Jet nightmare

I have had an account with jet since 1999, as off January this year i have been receiving numerous calls that my account has not been paid & i pay on the last day of every month i am still paying but seemingly my account has been handed over to MBD what makes me angry is the fact that 1 Jet has increased my account limit from R11000 to R20000 without a word to me & what i hate is the fact that no1 seems to know where my payments are going, I'm an old pensioner this is beyond annoying because i am now receiving threatning message's, it seems to be a dog show. No1 knows anything all they tell me is that i owe them money