The rules clearly state that all new messages require an answer or to be marked as spam within 24 hrs in order to qualify for SS. It doesn't matter who they are from or what they are about, no-one reads your messages, the system is automated and simply compares the time-stamps for receipt and response to determine compliance. If you mark that message as spam now, it should update your stats within a day or two, but it will not help with the badges already awarded.
If you don't want your purchases to affect your SS status, you have a couple of options.
1. You can use Auto reply to send a "thank you" or an "I'll get back to you shortly" message. This counts as a response for SS, but needs to be reset every five days.
2. You can create a few snippets with various messages and send quick responses that way in just 3 clicks, Snippets/Select/Send.
3. You can create a new, buyer only Etsy account and keep all your purchases separate from your shop.
Number 3 is the easiest option, once your buyer account is set up it requires no ongoing maintenance and you never have to worry about pesky sellers interfering with your SS rating.
