Nick here from Shopify.
Sorry to hear about this, it's never nice to have someone else take some of your ideas. I will make the appropriate team aware. If you feel a store operating illegally or in a harmful way you can review the Shopify Acceptable Use Policy here and also fill out an AUP report here, we investigate material reported to us and take action if it violates the AUP. This would be the best and most efficient way to let our team know.
Thanks again for letting us know and I hope this gets sorted out for you as soon as possible!
Absolutley no worries at all, what we're here for.
I spoke to someone on our legal team and they mentioned this help guide about copyright and trademarking which you might find useful.
Something else you can do is submit a DMCA notice from the link here. Once it's submitted the team will take a look and if you have any further questions you can reply directly to the email you'll automatically receive after submitting a notice.