I'm sorry to hear about your uncle's accident. This is truly a distressing situation.
In such cases, Saudi Arabian law typically holds the person responsible for the accident liable for the resulting damage. However, since the police have cleared the person who caused the accident, it complicates the matter.
The Kingdom of Saudi Arabia has very strict laws regarding Hit and Run accident cases under the 'Law of Traffic' regulated by the Ministry of Interior (Article 64), but if the person is not found guilty, the situation becomes complex. Moreover, under the Saudi Arabian labor law, Article 144, the employer is obliged to cover the cost of medical care for a work-related injury, but this might not be applicable here as your uncle is on a tourist visa.
A critical step would be to appeal the police's decision and provide additional evidence, if any, to hold the car driver responsible for the accident.
Regarding the medical services, the 'Saudi Patients' Bill of Rights and Responsibilities' under Article 16 states that "The patient shall have the right to get, to the extent the health facility potentials permit, full medical care, including pain relief, necessary diagnostic, therapeutic, rehabilitative and preventive services." It is concerning if the hospital is not providing the basic services due to the payment issue; this is something you should raise with the hospital administration and possibly with the Ministry of Health, if the hospital is not adhering to Patient's Rights.
As for the insurance company's lack of response, it is crucial to closely examine the terms and conditions of your uncle's insurance policy. If the insurance company is not fulfilling their obligations, you can lodge a complaint with the Saudi Arabian Monetary Authority (SAMA), according to 'Insurance Law of the Kingdom of Saudi Arabia' Articles 32 and 33.
However, please reconfirm this information from a licensed professional in the Kingdom of Saudi Arabia, as the explanation above is only for general understanding and may vary according to the complete facts of the case and the specific terms of the applicable insurance policy.
Please be advised that while every effort has been made to provide accurate information, this does not constitute legal advice and must not be used as a substitute for talking with a licensed attorney.