There’s an issue on Github for something like this - although that user was just using the event as the trigger *so I suspect you then get another event when it sends the text, so it sends the text again, which then generatres another event, which generates another text etc etc.
I’m using a similar setup to yours though, using specific commands, and I’m not seeing this issue. Feel free to compare your code with mine t try and narrow it down (see my Github).
This is a known problem and has been around for quite some time now. It’s related to the Telegram integration, running in webhooks mode. If you switch your configuration from webhooks to polling (platform: polling), it should stop doing that. There’s a relevant discussion here: https://github.com/home-assistant/home-assistant/issues/12774