Thank you for your question and for asking for me.
You need to file an appeal immediately, but under CA law, an employee who is fired for good cause is not eligible for unemployment. If they terminated you for calling off, they are now alleging that was their cause for bad work performance. Thus, you would need to file your appeal and present your evidence and witnesses that the calling out from work was your only time and that you had never been written up for any other employment issues at work and it was an isolated incident. You need to file your appeal before the deadline on the denial letter you received or you will lose your right to appeal forever. Under CA law, you must file your appeal within 20 days of the mailing date of the Department determination or ruling. See: CA Unemployment Insurance Code Section 1328.
Your appeal is really your only recourse here and here is a Guide to Appeals
for unemployment cases that can help you if you do not want to use an unemployment law attorney.
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