Payflex bad customer service!

I've been trying to get hold of Payflex for the past 2 weeks. I've tried calling every single day, I've sent 7 emails with no response.

It shows I have a payment due, however on the app and website there is no such payment so I'm not able to make any payment. They keep harassing me with messages, adding penalty fees and I'm so frustrated as I'm not able to make any payment to get them off my back and I'm not able to get hold of them either. Payflex has never debited my account as I settle all accounts in advance. I am SO frustrated. I'll rather be using Pay Just Now in future as they are much more reliable.