Firstly, sorry about your loss - I'd try to keep it short and sweet.
First and foremost - how to properly SELF EXCLUDE YOURSELF FROM CRYPTO GAMBLING WEBSITES
The trouble with crypto gambling websites is that you cannot really self exclude yourself from a site that lets you sign up again so easily with just a user/email and password ... since the transactions are anonymous then there isn't any proper regulation really!
Your solution? Read this:
https://bitcointalksearch.org/topic/is-there-a-service-that-lets-you-lock-your-bitcoin-for-24-48-hours-etc-5205451Next time if you have an urge to gamble away your Bitcoin you can lock your Bitcoin away from yourself -
this is a proper self exclusion tool - by locking your Bitcoin away from yourself for a specified time you define yourself - you won't have access to that Bitcoin until that time expires - this way for instance if you lock away 10 BTC for 6 months then for the next 6 months you won't be able to spend those 10 BTC even if you want to.
Edit (03-August-2020)
OP,
Were you aware you could even LOCK your funds away for 8% annual interest rate or more?
https://www.binance.com/en/lending/products?type=fixed
Imagine saving 36 BTC in this product, you would earn almost 3 BTC and you could say "Risk Free" without risking your balance. And your funds would be locked - cannot use them - only gaining interest. If you get a large sum again please consider this insteadNow,
Regarding your specific case
I would keep it short and sweet for you as I mentioned.
This is a very large amount.
My suggestion to you is to NOT use any forums, not use intermediaries - your best bet is to use a solicitor/lawyer and sue SportsBet.io for their negligence.
Only a lawsuit will yield you a result.
Am I speaking from experience? Absolutely.
I have used a lawyer in Curacao who sued a website which I cannot name - for something similar (although my case with them was not honoring a self-exclusion on the very same account I had with them) - that led them to pay me $7,000
I tried using SBRForum, AskGamblers, CasinoMeister - nothing worked ... only a lawyer was able to get them to pay me back.
So that's why I wanted to respond immediately to you by telling you - you are dealing with a loss of a big chunk here ... had it been 0.1 BTC I would use the forum likewise but you are talking about 20 BTC (over $220,000) - seriously - get a lawyer and start your case now.
Any other attempt to get this "resolved" - would only cause you to waste time, energy and it would be a futile attempt to resolve a case involving 20 BTC.
As in regards to SportsBet.io's due of care - I have to be honest, I personally don't like SportsBet.io (and many other forum members can testify and tell you I'm not lying when I'm saying it) - however you need to understand your case is not the best one out there because you opened a new account.
Graham Calvert in the UK tried to sue William Hill for something similar - he lost the case, and he also lost his family - I'd suggest to you to firstly lock your Bitcoin away from yourself so you won't lose more (and only this would help you to really self-exclude!) .... Secondly - I am not saying you don't have a case at all ... but a good lawyer might get a settlement/compromise or what's not - you won't get from this forum or elsewhere on the Internet!
Do it whilst this operation is still in business by the way, with the accumulating posts against them I'd be wary so if I were you I wouldn't waste time.
Oh,
I said "short and sweet" but looks like I got a longer post.
Anyway,
Hope it helps - good luck to you!!