We have had a direct debit we British Gas for about 10 years on a property, after a while radiators have stopped working and when the system needs flushing we were getting quotes for around £600.
We rang them up today to cancel our direct debit as it was pointless for us in our situation, we were paying £15.50 a month for this service. We rang 08457365100 (say no to 0800 "01698 802101") and asked to cancel, now here is the information that is key, they offered us 20% discount straight away when we said cancel, this worked out at £12.40 a £3.10 saving or £37.20 saving for the year. If you still want this service this seems like a great time to ring up and just instantly save yourself some money because it was almost immediate without even asking for it.
I reckon we could have got the price down further if it would have been a viable service for us. Good luck!