Rewarding your lost customers [slim]

I've noticed that common sense doesn't always govern decisions in business. I've often seen organisations spend so much time chasing new business that their existing customers are ignored and lost. It's a silly thing to do, not only because your existing customers are a source of current income, but it's also significantly easier to sell additional products to current consumers.
My ISP/Telco has finally introduced wires only adsl, which is a fiver or so cheaper than regular adsl. Great, I can hook up to that and save some dosh. But no, they require an engineer visit to take away the adsl wall plate, and replace it with a regular master socket. Then I can plug in some microfilters and I'm away. They'll charge me for this though, £105 quid. Now, the same work, is carried out if I bin the adsl completely, except they won't charge me. Smart. It's also actually cheaper to cancel the adsl, and then order wires only, that comes in at around £60 quid apparently.
The really silly thing is, there's no actual need to do any of this. They don't want the stinray modem back, I don't want adsl in any other sockets, and the face plate is only worth a few quid. Recon that's good practice? Stiffing your existing customer and not your exiting one?