Itc status ruined by Payjoy 's incompetence

I bought a phone with Payjoy and it's paid up fully. However now recently their name was activated in ITC showing that I still owe them, resulting in a lowered credit score and a bad reputation. I wrote several times to them and they take a long time to respond to emails and other messages. They are very unprofessional and very rude and even now my problem hasn't been solved.