I am having exactly the same problem although on since the end of June.
The number i want to bring over from EE (BT) is still live as I am paying £44 per month for it. I have been offered 4 port dates so far none of which have worked.
The funny thing is the number was originally owned by ntl who are now Virgin Media and it was transferred to BT then Plusnet then EE over a period of of about 18 years now i want it to go back to VM it seems far too difficult.
Can I say that given these falled port dates that VM are in breach of contract. Unfortunately after the second port failure i was two days outside my cooling off period so could not cancel without having to pay £200+ to end contract early. And believe me I am tempted to pay the money at times!
Oh and by the way the advice given on live chat to phone 175 to confirm my number has ported does n't work either. All i got was "oops you might like to try that number and try again". Perhaps the crib sheet in customer services needs to be updated - it seems this might not have worked for some time.
How are these problems escalated...