My father fell on his right knee at an Auto Parts store.?

About 3 weeks ago My father was at a O'Reilly Auto Parts where he slipped and fell from due an object which was on the floor. He witnessed the clerk laughing but he did not file a complaint. My father left the store but later returned because he began feeling a lot of pain a swelling to his knee and filed a complaint. Today we received a letter by the Claim Representative saying that they have completed an investigation into my dad’s claim but after careful review of their investigation, they must respectfully deny any payment on my dad’s Claim. My dad’s have been feeling a lot of pain to his knee and is thinking of going to a doctor to get it checked. He can’t afford spending money on a Doctor in the US so he is planning on going to Tijuana, Mexico. What should we do?