When you complete an offer like this, make sure to print your screen at every crucial stage (let say, when you click on the offer and when get the "reward" or achievement page) with time and date visible. Then, go to assistance on Supersonic offers page and report to them. At some point, they'll ask you to send a proof and you'll go with your screenshots. That shoud be ok. Happened to me several times with them and I eventually got the rewards.