The 10ppm is standard for a 0871 number but it looks like the devilish TalkTalk have gone further by adding a £2 minimum call charge as well as the 10p/min
The best suggestion I can make is ring 0208 8965000 which is their head office and say you've been constantly trying to get through but can't, you don't have internet access whatsoever (don't mention you are using dial-up) and you are extremely unhappy, etc and you wish to make an official complaint, etc.
Apart from that, I'd recommend moving to a more reliable ISP as I believe things can only get worse with TalkTalk due to their offer.
If you are unfortunate enough to have signed-up to their 18month minimum term contract then you could threaten to leave on the grounds that they are not fullfilling their end of the contract in providing a broadband service. If this is an ongoing issue (which I can imagine only getting worse) then there is the likelyhood that this may be your only way of getting out of such a long minimum term contract.