Hi – not sure what is happening with this site – I couldn’t get into it for a while, and now I’m seeing different versions of it depending on what browser I’m using! So hopefully this reply will get through, and you’ll be able to see it…
I hadn’t considered a management company in my previous reply. They are (probably) right, in that if they’re issuing a “self-billing” invoice to you with a payment, the tax point of your transaction is that shown on their invoice – later than the date you sold the room.
If that is the final invoice, then technically the time limit for de-registering would start from then – as that is the point at which you know that you’ll no longer have taxable business income. Although if you’ve been trying to get replies from HMRC since late July (and you’ve got evidence of this), it would be good justification if it turns out that you’ve missed a deadline. But you should now contact them and notify them that your taxable activity has ceased.
You then have two options. You could ask them to defer the deregistration for the six months and submit the next two returns as normal, assuming that you’ll have the professional fees invoice within that time. Alternatively, there’s nothing to stop you now submitting the June-Aug return straight away (you don’t need to wait until the first week of October) so that it gets through before your de-registration is processed – then you’ll just have to use the VAT427 to reclaim the VAT on the professional fees.