Spectrum Time Warner Spectrum charging $20 for having my credit card declined. New York

Spectrum charges $20 for a declined credit card transaction. I'm baffled. They're the first business in my 42 years of doing business where I've seen such a thing. I'm honestly aghast, and can hardly believe this. Someone pinch me, please, is this what corporate America has become? It costs them nothing, denoting the differences between a returned check, vs a declined credit or debit card payment.

On my spectrum.net account details page they call it a returned payment fee, but itemized elsewhere they call it a declined payment, declined being the correct terminology. This has happened to me on two occasions, two months in a row. Upon calling in the first time, after an hour of convincing them it was a ripoff, they removed the charge. On the second month, they said it was impossible.

I keep thinking I am missing something? Has this happened to anyone else? They insist this is their policy, for all declined payments, so if my credit card provider flags my account and prevents the card from being used, all circumstance comletely beyond my control, then I have to pay for that? Well, that is what it seems.

It is my view, SPECTRUM is ripping people off, and I have it all on tape. I asked every imaginable question to make sure it wasn't some sort of a glitch or that I wasn't understaning incorrectly. They are also claiming on tape, that the credit card provider has given them a reason code 521, which is non sufficient funds. In my experience in accepting credit cards in the past, they will sometimes give reason codes, but never did I see an NSF. Did I blink and the industry changed overnight like this? Is SPECTRUM giving me proper information? Are they really charging people for simply having their credit and debit cards declined? Someone please tell me I'm wrong. 

Thanks so much.