charged double for mobile bill

[iss1]

could anyone help me please. my original date for my mobile bill was on the 11th of each month. i just changed it to the 28th to work with my pay day for work. i've just looked and they have charged me double for my mobile bill. i paid this month on time which was june-july and so i don't get why i would be charged double when the date is still in july just a later date? its not like i changed the date to miss out paying in july... any help would be much appreciated:)

[PandJ2020]

Changing the date doesn't just change the date.

Your bill is completely recalculated (which is complicated due to monthly in advance charging).

The help says, "...your next bill might be higher or lower depending on the date you choose."

You can look at your bills (including future ones) to check the charged dates - it should be correct...