Bad service

I have a problem with payjustnow,their app does not work it keep denying my email address while they sending me emails when i report they respond but not helping whith the bug in their app they do not care about their customers i have been reporting no feedback about the problem and their app sometimes it work sometimes not it embarrasing when you do shopping only to find out its not working it was okey while its an abroad app since its South Asfica app never work properly what can we do about it?