Failed to check out with FIVE cards

As the title.

I am using different debit cards and credit cards for payment, and all of 'em are declined. I'm pretty sure is not the billing address or insufficient money issue. Is this a website issue? And customer service is basically a ghost. Anyone had the same problem before? How did you work it out?

One more question, is 7% estimated tax reasonable? Last time I check, there is only 4% sales tax in seller's state and my state, are they adding markup?