Anyone but BT

I called up BT on the 3rd of July to check about getting broadband, so they said I'd have it on the 25th of July (which was a bit slow but they needed to add the phone line, so that was alright). Not 5 minutes later, I got a text saying they'd (already) delayed it to the 1st of August, taking it up to a month.
On the 1st of August, the engineer announced that he couldn't complete the work, so set a new date for the 17th of August, taking it to 36 days after my original enquiry.
Later that day, I went off for a holiday, where I lost my phone. On the 17th, I waited in all day, having recieved no word from BT whatsoever. When the latest time for an engineer came and went, I called BT, who informed me that they had cancelled the order via text.
No reason was given, and no alternative means of sending the message were used. I called BT to have them reinstate the order, but the date has now been put back to the 6th of September.
While I acknowledge that this may not be the case for a lot of people, I've heard other reports of BT being slow and in some cases, simply unwilling to actually provide the services we pay for.

Has the phone line been installed?

hopefully you are not paying anything to BT at present ?

The problems will be both BT Openreach (which applies to most ISPs) as well as the bit of BT you deal with. BT Openreach give BT no better or worse as service than they do anyone else. I have had a positive experience with Plusnet (ironically, a BT subsidiary) but seen discussions on their support forum between PN and customers where it is clear that BT Openreach have been failing on hitting appointments, communicating, etc.

I switched from BT to PN because friends told me (and my own experience since has confirmed) that they are much easier to talk to both on the phone, by emails (odd, but decent ticket system) and on active forums that PN staff are involved in. I found BT hell to deal with though. However, both parties, and most other ISPs for BB and telephone have to deal with BT Openreach. Argh!

Not sure Virgin is great either. My brother has them and had similar problems to what you described in the OP.