LinkedIn Ads -- can't get refund for unused balance

I placed an ad with LinkedIn over a month ago. I was charged $50, but the ad only was placed frequently enough to incur a $6 fee. I have sent multiple emails to "customer service" but can not seem to get credited for the $44 they owe me. This is really frustrating and wasting my time.

I don't know why they had to charge me $50 up front in the first place (this was not clearly communicated. Not giving it back is terrible.