Add to Cart seems to be working OK on many other installs with the same version. Here’s some steps you can use to try to debug this:
1) Make sure MyStyle plugin is the most up to date version
2) Activate a different theme and test without your theme to verify if it’s a Theme issue
3) De-activate all plugins and test to verify if it’s a plugin conflict issue
We also have development services available if you are not able to get it working yourself.
Can you paste your WooCommerce diagnostic information here?
That will give us more info about your system.