unauthorised contract upgrade

found incorrect billing on my account found reported and filled in ***** form (J3-85u2k-kh01e) they refunded the difference but did not revert contract back to data like it should be every month wrong billing then I have to contact to rectify it why can't this be fixed I did not authorise the upgrade change it back to what it was or rather cancel it as it is not what I want or asked for then I can go to a service provider that will keep to its customers requierments