Instaflex is not scam. They have a decent product.
Check out Consumer Health web site. However...The sample free for shipping & then charge you later is common on the internet. But you should not be stuck. Visa should back you up.
Call them and explain situation. They will look into it. They did me with another web purchase. Now I read read read the fine print and post the date on my calendar that I need to call & cancel so I am reminded to call if I don't want more.
It's always wise to keep that that 'buyer beware' concept in mind.
Particularly with purchases on web sites! Good luck.