Analyse sales

I sell my products on another website called http://www.passiondelivery.com
i pay them a 20% commission for selling, albeit the prices on their site are 20% higher than mine.
I also pay them $120 per month for them to do Facebook advertising and newsletters to their followers.

I have attached the sales they do for us. You will see it has declined during the course of the year.
My question is: how many new customers per month am i actually getting from them? Or is it the same customers every month give or take.
The customers know my company and my company name and website. they could quite easily order from me directly if i no longer sold my prods on PD website.
Could i pull my orders from PD, redirect the $120 into my own advertising to get newer customers?

Your thoughts plse?

Cheers