iTunes Connect - difference between units sold and units paid out, plus Apples commision

I was wondering if anybody else noticed difference between units sold reported under the "**Sales and Trends**" section and what is actually paid out under "**Payments and Financial Reports**" section? I'm currently missing around 100 units, which equates to about $100-$200 loss. Does anybody know what is the best procedure to raise this issues with Apple, or better has anybody had similar issues and succeeded with Apple? Secondly, I also noticed an increase in the difference between "**Proceeds**" and "**Sales**" on the "**Sales and Trends**" section over the last year. The difference in the amount has been between 40-50% and recently as high as 66%. I thought apple only takes 30% commission. How come there is such a discrepancy between "**Sales**" and "**Proceeds**"? Thanks in advance.