Cheating by uncle of sharing profit of fathers share in business

My father and uncle entered into a 50-50 business partnership in 2007. There is no documents related to this partnership. Uncle hardly used to spend time in office. His son used to come and work with my father. In 2014 it was first time my uncle shared profit details. Profit was equally shared till Mar 2013. From there on it was shared in 3 parts. My father told that uncle will correct it next year. Unfortunately he died in 2015. Uncle says we are just investors in the business since Apr 2015, he will give 1/3rd profit and our money will be returned in 5 years. It's cheating. Please guide me.