Only Public Sector Units like HAL, BEL come under RTI. Other Public Limited Companies are private companies and do not come under the ambit of RTI.
However, these companies have to provide some information to government bodies like SEBI and RoC( Registrar of Companies). You can ask SEBI and ROC this information. RoC provides lot of information about companies on their site, you need to pay some fees and can get information immediately.
I am assuming here that the complaint was applied to a government body. You can use RTI to know status of complaint, usually this forces them to take action on the complaint. We have seen lot of such cases.
If you had applied for a landline connection to a government body like BSNL then you use RTI to get the status of the deposit money and when it will be provided. Usually in response to this they return the deposit.