Don't call yet. Read the letter twice.
The denial letter is evidence. Note the exact reason given, whether a contract section is cited, and the date — appeal deadlines usually run from that date.
Pull your actual service agreement
Not the brochure. The full terms PDF for your contract year. Find the Exclusions section and check whether the reason in your letter actually appears there.
Start a case log
Every call, every email: date, time, name, reference number. Appeals are won on paper trails.
Gather your evidence now
Maintenance receipts, technician reports, photos of the failed item. The company will ask for them eventually — having them ready shortens the fight.
Put your appeal in writing
Quote the denial reason verbatim, cite the contract section that supports coverage, attach evidence, and send it certified mail. Denial Decoder drafts this letter for you once it has read both documents.