They just called me up and said they heard about me leaving, then they gave me a better deal and because I chose a deal with only one TV box, the guy said take a picture of the serial number at the back of your second TV box and said it to the same number on WhatsApp
Thanks for your post and apologies to hear you are receiving calls you weren't expecting.
If you have given your notice then depending on the reason for the disconnection, the outbound team may well give you a call. I would advise against sending a photo of your serial number though as a precaution.
If you would like a better deal and have changed your mind, speak to the team on 0345 454 1111 so they can get the account updated for you.
I would be suspicious if they’re asking you to send a photo of a serial number via WhatsApp. Did you give them any personal information like account details &/or telephone passphrase? Did they ask for your full account password? If yes to any of these I recommend changing them immediately.