If your Union representative isn’t helping there just be more to this than you are reporting.

California has very strict labor laws that are very pro labor. Tell the Union representative you will be filing a claim as outlined above. And politely ask they kick it up to someone who can help you immediately. It’s why you pay union dues.

Self inflicted pain. Without a receipt you have no basis to prove a charge back.

Now that you have learned a valuable life lesson don’t make the mistake again. Keep your receipts until you reconcile against the statement.