My package is a tad shy of £50 a month, to which has to be added a small amount for a few chargeable calls. So I've set my monthly payment at £51. Each quarter my bill comes to within a pound or two of zero (last one was 99p in credit). If for any reason a significant credit or debit arises, I adjust the monthly payment to bring the next bill back in line. Eg, I got £30 in debit a while ago so increased the payment by £10 for 3 months.
Simple really, and I'm at a loss to understand why BT seem to make such a hash of it for some customers.
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