Nick here from Shopify.
Sorry to hear you got an allergic reaction from a product. Shopify isn't involved in any of the day to day running of a business or their return policies. Your situation does seem quite serious though. Your best bet in this instance might be to reach out to your bank directly about the next steps. There is a guide one of our colleagues wrote in the Community about what you can do, that you can see here.
If you would like to talk to someone from the Shopify support team directly, you can do that also from here.
|an hour ago|