I guess you are referring to the $19 withdrawn from your cc so many people are complaining about?
Please always read the T&Cs for vouchers. Nothing or almost nothing is really free in life. They don't give away $15 vouchers just like that (for people to join a free service). If you used the voucher, you accepted to start the paid membership,
https://www.smartyplus.net/terms (there is also a section about cancelling)
