You said that you factory reset the phone, but then reinstalled WhatsApp and Telegram. Both of those apps can take up a lot of space if you restored all of your chats. Your phone has only 8 GB of total storage, and of that, typically 4-5 GB are taken up by the system, which means that there's only about 3 GB of space actually available to the user. A lot of that 3 GB might be taken up by data from Whatsap and Telegram.
If you want to figure this out, do another factory reset, but this time do NOT install any apps, and see how much free space you have.
But as others have already said, this is an exceedingly old and obsolete phone (11 years old), running an Android version that is no longer supported, which at this point is riddled with unpatched security vulnerabilities. So the wisest thing to do would be to recycle it and upgrade to a more current phone.