Why do you guys always get the % increase wrong?
I don't know about "always", but in this case I got the math right and messed up the translation to English. We fixed the headline earlier this morning, thanks for letting us know.
Correct. An 11 fold increase is an increase by 1000%, but also could be stated as an increase to 1100%.
The latter option is what I was going for (e.g. "... increased to 1100% of the original price"), but have since realised it's just not a good option for headline writing.