I've traveled before ti europe, several times, and to USA. I've had several connecting flights and never went to Passport Control, but it seems in Frankfurt you will pass through passport control in all cases.
There are two situations that shall not be confused. When you land in Frankfurt from a non-schengen country and continue on to a non-schengen destination, you remain within the international terminal, and in this case you do not go through passport control (unless they have some special situation and need to place aircrafts to their non-standard booth). However, when you arrive from a non-schengen country and continue to any schengen country, Frankfurt is your point of entry into the Schengen area, and therefore you have to go through a passport control.
Note that the German Police said they have no idea why it says "-DE", they said there's nothing on their systems concerning me and they blamed Spanish Embassy since they should have saw that my flights are via Frankfurt. When I applied for the visa theh got my tickets and saw the itinerary. Also Luthansa should have not let me board the plane in Beirut.
I am afraid the embassy will take their hands away. They will claim that it is the traveler's responsibility to fly to (or to transit via) a destination that is allowed by the visa only. It is responsibility of the carrier to board only those travelers that posess valid travel documents. I think you might have better chances to win some compensation from the carrier.
Also should I contact the Spanish embassy and Lufthansa and ask for compensation?
I suggest to contact both. If you send them a letter, it will only cost you some small money, compared to the fact that your travel has cost you a lot.