A wifi booster only increases the coverage, extends the area where wifi is received. It's likely you're using more data for other reasons.
Also keep in mind, that one you start using the extender you will use up all of your data twice as fast. They all fail to mention that.
I got my extender, and it used up all of my data in two days.
Complete and utter nonsense.
The only way someone would use more data after the WiFi Booster installation is because they can now use the internet in areas where they couldn't before, so the increased data consumption is becasue of increased usage on the part of the customer, nothing more. Which means your data was used up twice as fast because YOU were using it twice as fast.