Hey there.
We’ve been working on that issue. After some tests, on iOS (iPad) and Android (Nexus 7 & Smartphones), we found out that your website have several javascript errors that probably disable the normal SliderCAPTCHA behavior.
In iPad, the Slider is drawn but not usable. In Android (using Chrome), the Slider is not loaded at all (with about ~20 JS errors in the console).
So our suggestion is you try to fix the JavaScript errors in your theme, and see if that helps. If not, please let us know so we can proceed with the debugging.
Thanks!