Help with statistics correlation?

I need help finding the right statistical method. My research is on is how ecommerce impacts financial performance. I have two data sets, ecommerce sales and overall sales. There is a clear linear relationship between the two, but I need to prove that ecommerce sales (x) impacts overall sales (y). I thought to use Pearsons product moment correlation coefficient which gives an r of .97. I know this shows correlation and not exactly cause. Is there a better method I could use?