Blocking account without notification

Good evening this is on behalf of my grandmother, she's had her jet account 10+years and paid her account almost every month. She did struggle at some point to pay but she managed yet she does not use her account frequently because she wants to pay to have credit available. BUT SUPRISINGLY today when she wanted to make a purchase at jetmart they advised her the account is blocked??!?! For a customer who paid for 10 +years they want her to pay the outstanding amount which is something around 400 then get a paid up letter and then go to reopen this is so upsetting for her that she wants to close her account now is this how jet treats their long term clients?!?!?