This site suggests that the official time limit is now 12 months
https://www.broadbandchoices.co.uk/ask-our-expert/can-i-keep-my-old-email-address-ask-our-expert
but you seem to have exceeded that anyone.
However, irrespective of what anyone on here writes, you'll clearly have no right to complain if TalkTalk simply delete your email accounts without notice. I recommend getting yourself one or more new email accounts here:
https://www.gmx.co.uk/
Use the 'mail collector' facility to get all mail sent to your TalkTalk accounts automatically forwarded to your GMX ones. (Then you'll only need to log in via the GMX site, rather than the TalkTalk one). You can then start informing all of your contacts about your new address(es) while, at the same time, not losing any mail sent to the old ones.