"31 complaints per 100,000 customers"
TBH that's spectacularly low for any type of business.
Of course, that doesn't include those who only complained directly to TalkTalk, not to Ofcom. It also doesn't include those who aren't happy but couldn't be bothered complaining.
Never had any experience of TalkTalk, but I do use another cheap-as-chips ISP, because in my neck of the woods it'd be pointless paying more for a service that can't possibly exceed 6MB/s (on a good day), unless OpenReach ever upgrades my local exchange, assuming they even know where it is.