Login issues

I am trying to login to enable me to change a payment date. I am unable to login as I do not have access to the sim card that relates to the contract. This means I can't get the security code that is required to allow me access to the online accounts screen. I have called and been through numerous chat bot phone menus but cant get through to an actual person. I dont want  a new sim. I literally want to push the payment date back by a week I don't feel it should be this hard. Send help before I loose my mind.