Currently, it is my understanding that there are issues with Dekko and it is not working on 16.04 (if that is the version that you are running). Also with the latest 16.04 updates there are issues with the browser on some sites (keeps crashing) and therefore webapps. The Telegram app though is working currently, but there are plans to completely overall it soon. What is the exact nature of the issue you are experiencing with Telegram?
Like advocatux said, what build are you on? As the above would explain the issues if you are on 16.04, if not add a few more details or replication steps.