There is nothing to do besides talking about your ban with group admin, if you were banned exactly in a channel or public group. BUT if you were banned due to your spam messages or because someone you chat with didn't like your behaviour and pressed button "spam" or somehow reported to moderators, there is one option you can do:
Search @SpamBot in your telegram, press start and then you will be notified what was the reason of your restriction. Also they provide information according to your case and show exact date when your ban will be removed.
All these actions can be applied just in case you can't sen how long I can'td messages to other people, excluding your contact list
Thanks, I never heard about this bot and now I know , when my ban expires. I hope topic starter also found a solution, but in any case you can change your sim card