It sounds like your account self-destructed due to inactivity. By default, this happens after 6 months but can be changed in your Telegram Settings.
However, once an account self-destructs, its data is all wiped and any messages/files are not able to be recovered.— Telegram Messenger (@telegram) January 24, 2021 #telegram
However, once an account self-destructs, its data is all wiped and any messages/files are not able to be recovered.— Telegram Messenger (@telegram) January 24, 2021 #telegram