No telecom provider can "increase" their tariff or take away a favourable service for six months since the announcement of a particular plan. If Tata Indicom took away your free roaming within this six months period, then you can write to their nodal officer or appellate authority informing them about the same. If they still don't resume your service then you can take the matter to Tata Indicom's telephone adalat (court). If it still doesn't work, then you can take them to consumer court and ask for compensations.
TRAI requires every telecom service provider to establish Nodal Officers, Appellate authority and Telephone adalat at their ends for easier redressal of customer problems.
If it has been more than six months since the announcement of free roaming service, then Tata Indicom is within its rights to withdraw the same.