Payment issues

[#1]

I have a problem with my credit card payment. I have already paid two milestones via credit card, the third and last milestone cannot be paid. Payment has been declined. From my bank everything is OK. Test purchase at Amazon, card works.
Why can I not pay the third milestone, although there was no problem with the first two?

Thank you.

[#2]

Hi Juergen,

We'll have one of our agents reach out to you via a support ticket to assist you with processing your payment. 

Thank you for reaching out to us.