In general, no, brokers being unwilling or unable to help facilitate a trade is a legitimate market factor. There's no fundamental right to have people trade with you.

It's would of course be a different story if the broker's unwillingness came from their participation in a price manipulation scheme. I don't think that's really plausible here, although I suppose I wouldn't rule it out given the crazy dumb things Robinhood has done in the past.