In India, even highly educated young man can not attend himself on a Govt work alone, take the assistance of relative or a social worker. Apply to Help Age India etc., voluntary organisations (Legal Services Authority is also a good option), they will come and help you with needed support. There may be many in Mumbai, and search google for such social service organisations that legally help poor senior citizens abandoned . There is Tata Institute of Social Seiences in Mumbai, they may help you through their students, as they have separate course on this problem.
File a hand written/typed simple complaint (no specific format available/required) for your maintenance before your District Collector/Deputy Commissioner (ex-officio Tribunal) under the provisons of Maintenance & Welfare of Parents and Senior Citiazens Act, 2007.