How long before assessment for ESA review?

I completed and returned my son's ESA review paper work in May 2019 and we have heard nothing since about a face to face assessment or anything. He is still in the support group but so many things have happened since I sent the paperwork in (now got an EHCP for one). I was going to tell them these things at the face to face and didn't want to confuse the process by ringing them, but seeing as it's taking forever what should I do? His original claim took 16 months before the f2f happened but I thought the review would be quicker.

Thank you for your reply BIS. We are moving house soon and will be in a totally different area, so I'll need to let them know about that anyway otherwise the letters will be missed and the f2f appointment will be miles away. I just don't understand the urgency they put on you to send the forms back when it takes them so long to do anything with them. It all adds to the anxiety of the process