Finally fixed after almost three weeks. Advice to anyone who loses Caller Display: Don't bother phoning customer services as whatever they try does not fix the problem, it just delays getting things fixed. Engineer came on Wednesday, saw problem straight away, ordered a tech visit, two hours later, problem solved. Thank you tech team!
Thankyou very much for your update.
Great news that Caller Display is now working as is should be.
If you do need anything else at all, pop back on here and ask away.
Have a nice weekend.