Organisation withheld pension benefits what action can I take

I had joined Kolkata Metropolitan Development Authority (CMDA),a Govt of West Bengal undertaking, on 25th, May, 1984 and had retired on 31st, March, 2008, from the same organization. At the time of joining I was under General Provident Fund Scheme, which was only scheme CMDA had at that time. When it came under the fold of CPF scheme, my name was not included as I was away from the office for the official training. Later they didn't include my name after repeated request. At the time of retirement they didn't ignored my demand. Official I had filed RTI twice which was not answered properly. I remain at present without my due pension benefits. The authority has detained my matured GPF fund for 5 year, however they had realised the principal amount without the interest due to me for the last 5 years. Kindly advice how I will get the above pending benefits.