It seems that the problem is indeed on the SMS provider in your country as I do not find any term that they block players from your country.
They should have an alternative way for this case, because it may happen for other countries too and if there is no alternative to solve this problem then coinpoker may lose some potential players from some countries with the same issue.
Using SMS for 2FA code receiving method is a risky choice because the SMS provider can have problems to deliver it to you and it can be seen by authorities too.
2FA should be on our devices only, and we don't have to rely on anyone, any provider to get the code for every time we need it. It is better for privacy too because authorities will not know what platforms you use and log in through SMS provider. There are other practical steps to secure privacy like using Tor but here we only discuss about bad choice with SMS for 2FA.
This method has another risk,
[Beware] Sim Port Attacks.
If it is for security purpose, I think email + 2FA will be much better than SMS verification.
I recommend 2FA for both email account and platform account, avoid SMS.
Applications can be open source 2FA like Aegis.
https://getaegis.app/