Ok so you are a legacy player.
No, your math is wrong. You say you have 11 days left. People who owned the 1.0 and legacy players received 10 free days, with this extention that would make 17 in total, aka 7 days from now.
As legacy player you also received early access which was extended by 4days if Im not mistaken.
Today is the last day of the Original 10 days, you received 7days extra and the 4 day early access extention = 11.
Looks like they gave you precisely what they promised you.