Blacky
If you have set up contact scopes correctly, the app should only be able to see the contacts in your phone book that you have explicitly allowed.
Did you select "don't allow" for contacts directly during installation or only later? If you initially allowed access (maybe by mistake), they are still stored in Signal (I can't say anything about Telegram). You can update this: Open Signal, click on "new message" scroll all the way down in the contacts and press "refresh contacts".
Maybe you can also check if you have set up Contact Scopes correctly: Long press on the app icon App Info>Contact Scopes (or App Info>Permissions>Contacts). There you should only see the one contact that you have approved.
Please note: If, for example, you have restored a backup of Signal and have already written to contacts in the past, they will also be displayed by name. However, this is the name that your contacts have given themselves in Signal, not the name that Signal pulls from your address book.