i want to cancel my monthly warranty

See instructions in Cancel or change the payment method for your AppleCare plan - Apple Support

If you're referring to AppleCare+, click here and follow the instructions. Otherwise, check the provider's store or website.

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You write you would like to cancel your warranty. It is basically not possible, and why do it too - it is a help if your product gets an error.

If you are thinking of changing or canceling your Apple Care Plan, look here:

Cancel or change the payment method for your AppleCare plan - Apple Support