This has to be taken up with the Shopify team. Here this is a community forum where technical questions are answered. I doubt you will get any solution here.
I’m sorry to hear this has happened, that is definitely frustrating and confusing. Based on our documentation, you have to follow a few steps and accept the terms and conditions in order for Shop Pay Installments to be activated on your store, so I’m not sure how this would have happened without your consent. I recommend contacting our live support team so they can investigate and get our payments team involved if necessary. We’re available 24/7, and when it comes to reaching out to our live Support line, I’ll provide some steps here to make it easier.