Due to a few issues with direct debits and banks being generally unhelpful whenever there is an issue I now refuse to use direct debits, going beyond that I intend to close all my bank accounts have all my income paid into the very nice and helpful local credit union I have just joined, whilst at the same time striking the first blow at the engine rooms of capitalism - (code for they have right peed me off and I'm feeling militant about it). As a result there will not be a direct debit facility available to me, not that I want one in any case. This is proving in the main to not be a problem as all my current bill payment can be made by BACS, (which will be available). Obviously Plusnet don't accept BACS but do offer card payments, but this needs t be manually actioned by me each and every month and would require me to make special provision for a single bill. In trying to find a compromise solution (and to minimise the £1.50 charge) I have proposed that I could make advance payments of £30 every 3 months for example, and as I only have broadband from yourselves this would cover it without requiring me to remember each month. Apparently this is not acceptable, as a result I am left with the option of finding a new supplier (I am just out of contract) that is prepared to reasonably flexible with payment methods, and particularly when it may be to the ISP's advantage, which I believe advance payments would be. For the curious I shall likely stay in Sheffield but migrate to the other ISP that doesn't over due the slightly immature Yorkshire thing.
Sorry, the manual effort required to allocate these payments far outweighs any benefit to us and leaves us open to risks such as excessive usage charges. Our billing system was never designed to do this which leaves us in the position you've described. The implementation of the new billing engine could do this, but it's not been included in the build due to extremely small demand and the risk of excessive usage charges.