Administrative negleigence ruining my life

Jet has ruined my credit score now I cannot get a study loan and a laptop for my school work. 2015 I opened a jet account after that I lost my job end of 2016 I told them but soon as I got a job in 2018 December I called them and paid up all the debts by March 2019 I did a once off payment now months later I find out from ITC that JET never updated my account with ITC now it still shows that I owe jet a lot of money. So it's their administrative neglegience that is costing me. Iam so angry with JET and to think I almost RE opened my account with them.