Payment After Termination of Phone Subscription

I was staying in Belgium for a few months so I had taken one of the mobile subscriptions from Orange. I was domiciled an payments should have been done automatically but for some reason that didnt work, so I paid the bills every months through the app. But now I have left from Belgium, and I had my subscription terminated about a month ago. I am yet to pay the bill for the last month, but I connot login on to the app or the website since my phone number doesnt exist under my name anymore. I keep getting reminders from the company to pay the bill but I couldnt find the right way to get in touch with them. What should I do in my situation?