FYI the person is almost certainly on the forums. Insulting them emboldens them and encourages them to continue. Especially if it's from you, Stef. It lets them know that what they are doing is working. The bigger the reaction, the better for them. Also it might be a guy or gal, or even multiple people and/or bots we don't know.
Stef removed threads about slow roll because "it became counter-productive". (
http://forum.shuffleit.nl/index.php?topic=1976.0)
It seems that if you or any other players express your/their anger, slow roll players may find it fun and continue their behavior.
By the way, I doubt the effectiveness of IP bans. If they are desperately spoiling the fun of other players, they can get another IP (if the ISP is giving out dynamic addresses), or use VPN, proxies, etc. Also, if they are accessing the game through a shared connection (public network, library / school network, etc.), it means other players on the same network may be affected.
I personally recommend messaging the administrators (e.g. Stef) and report the names to them privately instead of posting here.
At the same time, if you do not mind playing expansions and the longer queue time, you can check "Wait for expansions" in automatch options, and you will only be paired with paid players, who are not likely to be slow roll players. Anyway, no one is going to buy expansions just to troll more players.
If you have expansions already, I believe you cannot use the above method to ensure that you will meet paid players.
In addition, if this game requires a subscription (be it lifetime or not) to play, I believe it can filter out many slow roll players. Since this game is freemium, the slow roll problem is unavoidable except raising the requirements of registration (such as mobile phone verification), or AI/robots that intelligently block the users (such as finding out who is blacklisted by a lot of players and inspect the game log to see if he/she is slow rolling).
