If I were you, once I realized the money was missing, I would have accepted the loss and blamed myself for not paying attention. I would have never argued with the driver and passenger. Not only is arguing with people a violation of Law 9 of the 48 Laws of Power, you also invite a negative machismo response by being confrontational. You also seem to know little about Dominican culture, because you pleaded with other nearby Dominicans when, had you read the recent book I read on Dominican culture, you'd know that Dominicans consider you an outsider and your pleas to them will fall on deaf ears. Dominicans have loyalty to their immediate family first, then their extended family, city, province, and country. Being an outsider, you are the one who will be regarded with suspicion even if the cab driver took your money. The reason for this is because the DR has been invaded and occupied once by Haiti and twice by the USA, and they've had far more stolen from then than the money you lost. So as an outsider you will be held suspect and your pleas generally will fall on deaf ears.
Your decision to go to the police was another mistake, one I wouldn't have made.
Dominican police can be corrupt, and going to them with any problem sets the stage for you to have more problems. I come from a culture where talking to the police is taboo. The last thing I would ever do is go to the Dominican police over money taken from my wallet. I wouldn't ask the Dominican police for help even if I got jumped on the street and got my ass beat. I would go to the hospital, get treatment, reflect on how it happened, and vow to never let it happen again, but I would never, ever, go to the Dominican police because the police in this country are corrupt and I would draw unwanted attention to myself and could get into more trouble.
I'm assuming like most men, you keep your wallet in your back pocket, right? If you do, that was another mistake. My wallet always stays in my front pocket near my groin. Much harder to pick pocket or for the wallet to slide out. I would also consider buying pants with zip up pockets to. The reason the Dominicans implied you should be happy you still had your wallet is a cultural thing. Dominicans have tough lives, and many have resigned themselves to being poor and powerless. Therefore, Dominicans tend to look on the bright side of things.