Yevhen Horbyshyn

This plugin allows you to send Telegram messages when posts are published. You can configure which post types trigger notifications, and customize your bot credentials and chat ID.
<h3>External services</h3>
This plugin connects to an API to send message to Telegram messenger.
It sends the message every time new post of chosen type added. 
This service is provided by Telegram Messenger Inc “Telegram”: Terms of use – https://telegram.org/tos, privacy policy – https://telegram.org/privacy.

HQFam Post Notifier for Telegram

Send Telegram notifications when WordPress posts are published — simple and configurable plugin.

iTRON

This plugin allows to send Contact Form 7 messages to your Telegram-chat. For this you need to make several simple steps.
<ol>
<li>Create the Telegram-Bot and save the Bot-Token parameter on the settings page Contact Form 7 – CF7 Telegram or to <code>WPFC7TG_BOT_TOKEN</code> constant.</li>
<li>Paste the shortcode <code>[telegram]</code> in your contact form template for activate sending to Telegram.</li>
</ol>
Now you can to add users or group to subscriber list. 
To add a user send the <code>/cf7tg_start</code> command to your bot. 
To add a group add your bot to the group and send the <code>/cf7tg_start</code> command to your group.
After this, you will see the requests on the Contact Form 7 – CF7 Telegram settings page. Approve or decline them.
<h4>Hooks and constants</h4>
Filter <code>wpcf7tg_skip_tg</code>. 
Use for skipping sending message.
Filter <code>wpcf7tg_markdown</code>. 
Use for customizing markdown tag set.
Constant <code>WPFC7TG_BOT_TOKEN</code>. 
Use for define the bot token value in the program files.
This plugin uses <a href="https://core.telegram.org/api" title="Telegram docs" rel="nofollow ugc">API Telegram</a> and makes remote HTTP-requests to Telegram servers for sending your notifications.

Contact Form 7 + Telegram

The best plugin to connect your CF7 form to Telegram. This is a lightweight plugin that also parse your HTML tags into markdown to format well done the output messages. 

Good job! 

A lightweight plugin to connect CF7 to Telegram

This plugin allows to post CF7-messages to you through Telegram-bot. Just use shortcode [telegram] in your CF7-form.

HQFam Post Notifier for Telegram vs Contact Form 7 + Telegram