I can't imagine that a snarky reply to email would be a violation of the Terms of service. I was banned last summer because of my public criticism of their royalty reductions, but they don't have to have any reason to close your account.

They do have to have a reason to withhold money owed to you. They also have an obligation to provide a 1099 if you are in the US and earning more than $600 in 2020.

I still don't have my 1099 from them, but when I wrote in early February I was told I would get a paper copy in the mail and it would be a few weeks before I received it. They did reply promptly.

I think I'd take the tack, in more emails, that you want to have details about the basis for withholding your earnings because you are planning to take legal action if it isn't paid and are sure you haven't committed any of the violations in the TOS that allow Shutterstock to withhold earnings. I'd also point out that the payment for January is owed by February 15th.

"If your account is terminated for a breach of the material terms of the TOS, in addition to its other rights at law or in equity, Shutterstock shall have the right to retain any royalties and/or other compensation otherwise payable to you hereunder as liquidated damages."

As far as the video still showing up, it may not be for sale. It takes them a long time to remove all vestiges of content, but there's a while where it show up but can't be put in a cart, or if it can, can't be purchased. My portfolio still shows the sets even though they've scrubbed my account (done last July)

https://www.shutterstock.com/g/jsnover/sets

Their IT isn't the best

You could try messages to the VP of Content via LinkedIn if the emails don't get you your money and 1099.

https://www.linkedin.com/in/pauljbrennan/

You could also consider kicking up a stink on social media if the emails and LinkedIn messages don't get you anywhere, but they will quickly block you, leaving hashtags as your only way to give them a public scolding.