If I were Castro, it would be worth the payment to help out Iran. The risk is little, we would have to take a overt stand against Cuba and admit we are meddling in Iranian politics. When if we want the signal to get to Iran we transmit it from the Arabian Gulf, instead of confronting Cuba.
This is an American business doing business in America apparently being targeted by a foriegn nation. What would you do if you went to work, and the power, phones, and water had been shut off? Your company could lose business, fall behind, or eventually go broke. This is one of the few things that governments are specifically designed to prevent, unfair interference. If this were to be proven, Cuba wouldn't have a leg to stand on legally.
At the moment we only restrict ourselves from doing business with Cuba, but that can change in a heartbeat if they want to play dirty.