You can only play at physical casinos that are licensed in your country, and actually they are only for non-Muslims. Casino companies are more compliant with government regulations than religious laws, so they will continue to operate even in a Muslim-majority country as long as your government grants the license.
If I were him, I would try to play at physical casinos instead of online casinos because I think that will be safe for me and I do not break the rule of my government.
If you try to read again the case of the OP, He wants to play online Casino to have a privacy since his religion has a very strict law against gambling so his only option is to play online to avoid being caught by there religion officials.
The problem of OP is very hard to solve since he didn't mention his country and the name of Casino that he try to access so that we can verify if there's really a problem on the Casino or on his ISP. I believe the ISP is his problem since the government can regulate online gambling by banning all the online gambling site through ISP provider regulation.
The problem seems to be from the Internet Service Provider. Maybe with their help issue can be solved, but it looks like OP isn't interested to reveal his difficulty to access a specific gambling site. Apart from this there can also be issues with gambling platforms not allowing users to access from specific regions, here his country is not in the list. Then the option is to use mirror links provided by the gambling site. Every gambling sites doesn't provide it, but with Stake there is mirror links provided.