Unity rewarded ad memory leak

Hello there. I added a video ad on unity. My game is a level-based mind game and ads are loaded into memory at each level. Each level is set as a stage. As the level progresses, the ideo ad loaded into the previous memory does not disappear and gets on top of it every time. I keep track of the ram usage and it keeps increasing at every level. After a while, the game shuts down. What can I do?

unload the previous video

how do i do this

destroy and then unloadunusedassets