If you are currently a VM broadband customer and wanting to switch to the Full Fibre network then you will be on VM's older DOCSIS (Fibre) network which uses coaxial copper cables. The incoming VM coaxial cable carries both the linear broadcast TV channels & the DOCSIS internet. You can receive broadband speeds up to 1Gbps on this network. VM won't allow existing customers to upgrade to the Full Fibre network from the DOCSIS network at present.
Full Fibre (XGS-PON) is fibre to the premises and is VM's newest network currently offering speeds up to 2Gbps symmetrically and will be capable of 10Gbps symmetric speeds in the future.
If and when it does become available to existing VM customers then they need to be aware that the full fibre to the premises network uses VM's latest router, the hub5x, which isn't compatable with the older DOCSIS network and it doesn't have modem mode. There is also no landline service on the full fibre network. On the new network the TV service (if taken) is carried over the internet so there is no recording facility either.
You say that, 'I filled the form, set up another direct debit, got email from them about installation date (31 July) and Contract information Sheet. It is now 05 Aug and nothing happened.'
If that's the case then it seems likely that the new order has been cancelled for the above reasons.
I suggest that you could try calling the pre-installs team on 0800 052 1734 and ask them what's happening. They are open 8:00am to 9:00pm Monday to Friday, and 8:00am to 6:00pm Saturday and Sunday