What Causes Stiffness In Arm Along With Slurred Speech Post Brain Stroke?

My son is a heart patient. He had a mechanical valve placed when he was 23. He had a stroke last February and it took out the left side of his brain. Hi is doing real well all is back except some stiffness in his right arm and his speech is slow but coming more every day. In October he had a seizure and ended up with a brain bleed. In trying to get him on the right medication they have tried two other seizure medications which have failed and now they have him successfully on Vimpat. Bad things is Insurance wont pay for it. I am getting the run around by the doctors of who should take care of the pa to get it approved the primary says Neurology and they say the primary. We are paying out of pocket at $198 for 14 tablets the insurance co wants me to keep trying other meds that they will cover. We were in danger of loosing him twice I m not willing to keep letting them use my son as a Guinea pig. Is there anything I can do that I m not doing or is there any discounts on this drug? Im so frustrated that the insurance co. wont cover the drug prescribed by his Doctor. I cant see how they are saving money when they have had to pay for life flight twice and all the professionals not to mention hospital cost when they do these trial drugs. Makes no sense.