It may simply be that I'm having a bad day, but I'm no longer entirely sure what I pay my ISP for.

I'm currently involved in a long, irritating and deeply dull arm-wrestle with my ISP (internet service provider). I'm trying to get it to pay me a rebate on the cancellation fee I paid when I moved house, having subsequently signed up for another 12 months of its tender broadband ministrations.

The company – which will remain nameless – accepts that it owes me the cash, but has failed to pay up. For nearly four long months.

(It also delights in failing to answer emails, has a bewildering array of departments and sub-departments, and isn't shy of exposing its users to lengthy bouts of offensive hold music.)

It's probably my own fault. Rather than listen to the views of the PCA readers we surveyed last year, I chose my service provider based solely on the monthly fee. As a consequence, my (admittedly reasonably priced) ADSL broadband is 'provided' by a small company, and it palpably can't cope when things go wrong.

Which may be only to be expected – but I'm not entirely sure what my ISP does for me, anyway.

Recently I had connection problems. After indulging in many and several frustrating emails and calls (most of them involving helpful suggestions along the lines of "Have you switched on your PC?"), the company was kind enough to arrange for an engineer to visit. A BT engineer.

And there's the rub. Because, of course, unless you live in Hull, your ADSL broadband is supplied along a BT phoneline. I use my own modem and router, I have a separate landline phone account and, with the odd spectacular exception, I'm not a total dullard when it comes to computers. (And yes, I'm going to get cable just as soon as I can.) Bring on WiMax.

So what am I paying my ISP for? It collects my money and is the first (aggravating) point of contact when things go wrong. But aside from marketing itself, spamming me and doing the (piss-poor) admin, I don't understand what it does for me.

Can anyone enlighten me?