If I am understanding everything correctly, the monthly cost for an 80Mbps SoGEA broadband line is £45 from AAISP (500GB quota level), £34.99 from Zen, or £30 from IDNet. That is quite a difference just for customer service and modem options (depending on contract lengths).
My current experience of trying to contract AAISP's sales department suggest they are not worth it. If they are ignoring me when I am asking to give them money, why would they be interested in helping me when they already have it?
Is the quality of service with FTTC or from any of those providers such a problem that I should expect to need to use customer services often? I have been with Sky since then bought O2 Broadband which was a long time ago, and only once can I recall ever having a problem
I contacted AAISP sales using IRC (under Help on their website), within seconds I was speaking to a staff member who then immediately called me. I contacted them again regarding a couple of things and the same response with emails answered in minutes.
It could be your email isn't getting to them or is going into SPAM.
IDNet service is good as I've used them, although left them due to them using Zen backhaul and issues that was creating for me which they couldn't fix. Note that IDNet is £36.00 a month with VAT, the £30 is ex VAT.
IDNet (and AAISP) are not large ISPs so you are less likely to be held in a queue or get typical first line support responses of "turn it off and on again".
Without knowing in advance if you will actually need support and for what faults you may have, you can never really know which is going to be the better ISP before joining.
Basically you are wanting the best service and support at the cheapest price, and don't we all, but its usually a case of picking one, you don't get to have both usually.
If price is important and you want the cheapest, then IDNet will be fine. If you want the most reliable and the most likely ISP that will go the extra mile to sort out problems that you may never have, then AAISP might be better.
Just forget Zen and make a choice of two. Price and desire, do you desire the reputation of AAISP more than saving on price by going to IDNet?