I was avidly reading IntelSlav Z etc. at Telegram and my phone available memory gradually disappeared until my phone wouldn't function.
It turns out Telegram defaults to storing media on your phone. It is very easy to fix. Instructions are here:
https://www.guidingtech.com/top-ways-to-free-up-space-in-telegram/
It works like a charm. Super easy to fix. I don't know why you would till have the problem. Just follow the instructions in the link.