Slow speed, intermittent dropouts, breaks in the signal, no signal on some or all devices or no internet access might be caused by Wi-Fi interference from other local networks, which can also lead to a permanent reduction in speed. No ISP can be responsible for your local environment, this is mainly a byproduct of the popularity of Wi-Fi.
Generally speaking, the 2.4GHz band suffers a lot more from interference than the much faster 5GHz band, but the 2.4GHz one can sometimes have a better range, but this all depends on your local area.
In other words, I try to help you optimise your Wi-Fi connection. If you would like me to help you, please can you specify the make/model of TalkTalk router that you are using?
