Bad and good
For several years now I have been on Plusnet (owned by BT, but operated independantly) I have had good service, and since I do a lot of my surfing after midnight, their 10Gb deal works out very good for me. Only spoken to them a couple of times - once for a phone line fault, and once to set up a service for someone else, and found them knowledgeable and willing to accept that I did not know what I was doing.
I also bought a smartphone a month ago on Orange - I didn't particlularly want Orange, but did want the phone offer. Orange were utterly useless, as I was unable to set up an account to spend money with them! Passed me from department to department, never called back, refused to accept that what I told them was possible, and seemed to be located on the far end of a very cheap VOIP link.
Sent off for a new sim - that didn't work either, as it was impossible to find out what it's phone number was until you had put money on it, and you couldn't put money on until you knew the phone number.
I didn't bother talking to customer services, just binned it and got a t-mobile sim, which worked out of the box, no problems, set up account, paid in money, made calls. Sorted.