If you have you know the chances of your getting any satisfaction is slim or none. That's been my experience as well. And as a result, my motto is don't bother.
Online surveys are not meant to be fair. They are primarily marketing/advertising vehicles (for example the surveys that have you watch commercials you've already seen on television). Your just a widget for for getting products more exposure. It's your eyeballs they want and that's about it.
Unfortunately, the survey sites themselves are pretty much just shills for the advertiser/marketer. Although the survey sites will be quick to fault you for not paying attention, or booting you out if you appear not to be watching carefully or taking the proper amount of time to take a survey they are very much lacking in any similar care when it comes to the underhanded antics of their clients.
Take for instance the circumstance where you've completed a survey. You've even gotten a "thank you for completing the survey" message at the end of your efforts. Then, when you are returned to the survey site you are informed that "we have enough respondents for this survey, thank you." You've taken lots of time only to go unrewarded. Justifiably angered, you contact the survey company to complain. Invariable you get an automated reply (sometimes a reply from a person) that says, basically, tough luck. Oh, it'll be couched in less direct terms, but the meaning is the same.
Don't Expect Changes
What has been most frustrating to me is that, technologically speaking, it would be very easy for the survey companies to adjust matters so that if you are in the midst of taking a survey you are locked in until you complete it. In other words, no more than the actual number of survey respondents are allowed to even take the survey. This way, it's not a race for who finishes first, but a more fair system that says if you start the survey and complete it we will give you the promised rewards. At the very least, if the total number of surveys are taken, then those who are in the middle of completing it should be notified so they don't waste any more time.
Is this about to happen? Not a chance. While a survey site like Mechanical Turk makes a sincere effort to let you know if a survey has reached its quota, and lock you in if you accept a survey so you can finish it and are sure to be rewarded, the commercial survey sites don't do so, and are not inclined to in the future.
So, should you bother complaining? Don't bother. Being unjustifiably aced out of rewards you've earned are just part of online survey taking. Just grin and bear it.