I am working in an IT environment as an IT consultant. We had a scheduled maintenance on Sunday at 5am. As a team we decided to create a skype group chat that we would use to communicate among team members. On Sunday at around 7am I missed a call from the client and when I tried to call the client back with no avail. I checked the group chat and I found that the client already made a clear instruction that my colleague should be the only person that should deal with the issue. Now, my company decided to charge me with subordination and their verdict is that I should be given a final warning. The chair of the hearing insist that I should be have answered my phone, can this be the reason i should be given I a warning.

I would like to appeal to this warning. Please share the opinion.