What Customer Service?

I moved to the UK 15 February 2019. Prior to this I arranged for my number to go onto prepaid. My debit order bounced beginning March, since then I have been trying to make contact to get banking details to do a manual payment, I still have a data modem and my sons number on the same account. You CANNOT call from an international number to the number listed on the website and you CANNOT send an email from a different email address to customer services. I WANT TO PAY MY ACCOUNT.... the data and my sons phone has been suspended but I cannot get to pay it. I get an email saying they will call my number... which is on prepaid and only accepting whats app calling, they won't phone and international number and you get an automated email when they finally reply saying they will call and the email address to send the manual payment POP but NO BANKING DETAILS TO PAY - not even on their website. I log on to my profile and only my number is available is mine .... not the other two that are linked to my number on the account.... cannot view anything. The information on the profile is so limited I can do nothing to manage my accounts.

All I need is BANKING DETAILS or a NUMBER TO CALL FROM AN INTERNATIONAL NUMBER