They didn't steal your drops. Sounds like you failed to open the first before gaining the second. Rankup packages haven't stacked since Taken King launched in Sept 2015. Gotta open the package before ranking up again to avoid losing the first package.

I did no such thing! If you read our Rewards policies (which are the same for all factions) you would know that, 11.A. If you do not claim your first package, then your next one will be given away to the next Guardian. 11.B. We give you rewards to thank you, but we are not required to give you anything. 12.C. Rewards are subject to resource limitations. I stole nothing from you. Your reward was most likely given to another Guardian. Or recycled.... Or used by me.... Most likely me.

Did you go from level 1 to 2, or level 2 to 3? If so, you don't get anything. 3 to 4 and onwards you should.