My base is in level 11 and other raiders are 16 level base and they are taking away all my resources..

When you get to the middle ranks your base will be a target for others. It is hard to avoid being attacked, generally there is no long term damage but loosing all your resources makes it hard to progress. If you can, move somewhere away from the attackers.

There are a few other tips here to try

https://www.appgamer.com/last-shelter-survival/strategy-guide/how-to-stay-safe-in-last-shelter

Join a Top 15 Alliance and the alliance will protect you till you reach 16 at least.