@CheHackman1
You can’t, except by letting your membership run out, waiting until the day you want to pay on, and then resubscribing.
But note that if you have more than one membership renewing on a certain day, the payments may be staggered over the following days.
However (and the passive voice hides many sins) if Now unilaterally changed this on you without your say-so, get on Live Chat and require them to change it back.
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Please bear in mind that generally we are all customers like you, and so can’t help with billing or other queries that only Now can answer. We can try to point you in the right direction though.
