I want to appeal the decision but I'm not sure if I have the grounds to? I asked if they had already made their decision and they said yeah and the letter (written warning) was in a sealed envelope. Have they not followed the correct process here? I got called in again yesterday as it seems other people are jumping on the bandwagon - I've never felt this bad in all my life!
The correct process should be that they have the disciplinary meeting with you, ask you to leave (or they leave) while they make their decision, then ask you to return to the meeting to hear the outcome of that decision.
If they've come to the meeting with a sealed envelope and immediately handed that to you without having considered your input to the meeting, it's wrong because they had clearly already decided the outcome prior to the meeting.
See what the company's disciplinary process says. If they've failed to follow their own process, it's an even bigger no no.
Were you given the opportunity to be accompanied at the meeting?