one or two points to note, fair enough you are frustrated but:
2.i believe Mesh has a national rate support line so its only 8p peak 4p off peak, the money they receive via BT is not very much at all. you probably spent at most a couple of quid if you called in peak time
3. anyone who's ever worked in tech support will confirm that somebody telling you what they think is wrong will always get their back up, and in any event they have the right to do confirmation checks on the problem to find out where the problem lies. tech support frequently get told 'this and that isnt working, please replace it' only to find out that it was a minor software fault instead. obviously this isnt the case in your situation, but they need to check anyway.
4. i wouldn't find this delay reasonable either, as 5 days for somebody to just get in touch for a repair is a long time to be without your pc. focus on this as they should be able to organise somebody sooner, parts permitting. perhaps they could deliver the replacement for you to install as a speedier remedy. i would also request a different make of hard disk to lessen the chances of this happening again.
was this similar to the first time you had a replacement?