What to do if mail with social security has been opened when delivered?

I received some mail from an insurance company who decided to use my social as an identification number...WHY?! Anyways, that mail was opened (as in i could take it out myself without having to open it) before i received it. What do i do about this? I have already purchased ITAC Sentinel Plus Identity Theft...but it will cost 12.99 a month, and plan to go make a big complaint at the post office. Is there any way I can contact social security about this?