This has happened a couple of times now and is winding me up but when I have a refund applied to my account before a payment is taken, the amount of payment taken is reduced by that refund amount. e.g. statement balance of £500 set on 12 March, refund of £50 applied 20 March, payment taken on 31 March of £450 NOT £500. Therefore the amount due the following month is increased by £50 as the refund went on the previous statement that it wasn't connected to.
I know in the grand scheme of things this is VERY minor but why is it happening??? Surely the statement balance is set in stone, or on paper/pixels at least, and shouldn't change. If I don't realise the refund has affected 'this month's' payment and I have a surplus in my account I could accidentally spend it and not have the money hanging around for next month when it has now become due.