Most platforms have a "Request a Title" feature. If enough people ask for "Ganga" on Aha or Netflix, they might acquire the digital rights.
Users searching for "Free" access generally encounter two types of sources: Legal Ad-Supported platforms and Illegal Piracy networks.
Platforms like Olx or eBay often have sellers giving away old DVD collections for negligible prices (or recycle shops). You can digitize it yourself for personal use.
Very old Telugu films (pre-1960s) may be in public domain. Check Internet Archive (archive.org) – search "Telugu cinema".