Block special characters and numbers

Hello,

I am using WooCommerce with the product add ons plugin and I was wondering if there was a way to stop users from typing in special characters and numbers into forms. I have a global add on that allows user to add name personalization to their product and under group I have the only letters option but it still allows them to use special characters & numbers.

Is there anyway to stop this?

https://www.ads-software.com/plugins/woocommerce/