All the comments and shares on the Soundcore page are public. So by comment / share Soundcore you implicitly expressed interest in Soundcore.
Then any bad person will PM you saying you won, you’re highly likely to reply back.
Sufficient portion of folks don’t check and reply, the profits from that pay the wages to do it.
Ideally Soundcore would not use Social Media for likes / shares / comments.
I’ve just checked, the loophole of find followers seems closed.
What you can do is go into your Facebook privacy settings and decide if you want everyone to see everything. For example do you really need
Another tip is to have dedicated Facebook account just for Soundcore Facebook, so if you get an email not related to your Facebook page pretending to be from Soundcore, it’s obvious.