No, you are right. The 3 day notice is not valid. It wouldn't be anyway, because you are supposed to receive a 90 day notice to vacate.
I have done a lot of work in this area, but first you need to tell us whether you are you a tenant or a former owner as your rights depend on your status. Seems like if you got a 3 day notice you are a former owner. In that case as soon s the sale happened the new owner's agent could you send you a 3 day notice to vacate. If you are a tenant they would have to send you a 60 day notice or perhaps even honor the remainder of your lease. If you lived in a rent controlled area with just cause needed for eviction then a change in the ownership done';t consist just cause and they might not be able to evict you.
Hope this helps and good luck.