Hey there, @user_5hla9r! I am very sorry to hear about the experience with attempting to change your bill due date. You have certainly exhausted lots of options with attempt to change everything online. There are a few things that might prevent the account from changing the billing due date, and they can be found here https://www.xfinity.com/support/articles/due-date-change.  A few things to note,  To be eligible for moving your bill’s due date, you must have completed at least one billing cycle, and your bill must not be currently past due. Once you change your bill’s due date, you will need to stay in that cycle for at least six months. We can certainly explore any options if your account does fit the requirements. 

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