I assume you've checked via TalkTalk Mail webmail that there are no Rules operating to divert or block incoming messages?
What's the source of the emails - the email domain of the company? Domain is the part of their email address after the @ symbol.
If you find a previous email and in TalkTalk Mail select the email and then from the triple dots More actions menu select View Source and you'll see the normally hidden email header.
Find the lines:
Return-Path: <email address>
Received: from Sender ([XX.XX.XX.XX]) by mx.talktalk.net with SMTP (NB there will be several Received: lines but only one that ends with by mx.talktalk.net with SMTP)
From: Name <email address>
Return-Path: The email domain enclosed in chevron brackets will tell the TalkTalk inbound mail servers where to find the Sender authentication SPF file
Received: from The Sender name and the IP address enclosed in round and square brackets will tell us the mail sender communicating with the inbound TalkTalk MX server
From: The email domain enclosed in chevron brackets is the source email domain
With the above information a check can be made to see if there's an obvious reason for mail not being received.
Have you checked with the source of the emails to see if they are aware of any bounceback failure to deliver notifications and if so what the description and TT three digit error code was? Then see if they are aware of your email address being placed on a suppression list (a no mail list) that would mean their mail servers have failed to deliver after retries and as a result will send no more emails. If they do operate a suppression list then have them clear your email address from that list and you'll get their emails once more.
