Review the support article below. If they have already shipped the replacement phone, you will not be able to cancel the claim and your current phone will become unusable.
If you cancel your claim because you found your iPhone, you must set up your iPhone like a new device. You'll be asked to create a new passcode, Touch ID, or Face ID. To get the data previously stored on your iPhone, restore your iPhone from a backup.
You can't cancel the claim if a replacement device has shipped. If you find your lost or stolen iPhone after your claim has been approved, you won't be able to use that iPhone again.
File a claim if you have AppleCare+ with Theft and Loss coverage - Apple Support
You can also use that link to check the status of your claim and it includes contact information both by telephone and online. If you have not heard back by contacting them online, then give them a call.