I understand the issue you're having and will try my best to assist you with that.
I checked your site from mobile and can confirm that I can switch to USD, SAR, and AED without any issues. Also, the price is updated according to the conversion rate. Please check this video for a better understanding: hidden link
Could you please clear the caches from your site and browser and try again?
If the issue persists even after that, please let me know how/where should I check to see the issue. I will check accordingly and let you know what to do next.