Why is billing / making payments so painfully difficult?

Been on again/off again with the pdf services api for the last 18 months, and returned to a new and hopefully finalize project soon.  I "used up" my 500 monthly credits although I extracted many fewer docs.  I guesstimate 150, 2-page docs.

I've looked around for 30 minutes and there is either a 1) free section or 2) contact sales for  enterprise, but no place for "retail" sales.

Isn't there a section which takes credit cards?  I previously recall doing this directly and through amazon marketplace which has subsequently been cancelled.

Please advise as Adobe is my first choice for around 1,000-10,000 docs month initially, a relatively small amount, I know.

Thanks in advance.