JET STORES IS THE WORST EVER

My father has a Jet account, which he has not used in years, But somehow he keeps on owing Jet thousands. After numerous calls and went to the Store in Atlantis and they not able to assist. We have asked for detailed statements nothing yet. But they keep on calling saying he owes over R3000. So we assume someone is using the account within the Jet company. that's why they unable to sent detailed statements explaining these amounts owed. did anyone experience something like this before? Any assistance as to what we can do?