The Developer is not likely to be much help here and may actually be part of the problem.
MrSaffron is only partially right with his reference to "Post Office Database", otherwise known as Postal Address File or PAF. This is sold out into the market in a number forms but generally with a software interface such as Quick Address or QAS from Experian.
Before an address appears in PAF however it is the Local Authority that have the statutory duty to Name the 'Street' and Number the properties that are accessed off that Street. This process is known as Street Naming & Numbering or SNN for short and conforms to BS7666 Spatial datasets for geographical referencing. The result is a Local Land & Property Gazetteer or LLPG for that authority's administrative area which is then amalgamated via a National Hub, now called GeoPlace.
Under current codes of practice newly created addresses are passed to Royal Mail's Address Management Unit for inclusion within PAF and allocation of a Postcode. Yes folks the Postcode is not controlled by your Local Authority so please don't shout at them if you are having problems, but do seek advice from their SNN Officer / Address Custodian.
Royal Mail allocates and then uses the Postcode to manage its delivery rounds and may change any or all of it to suit its own purposes e.g. some years ago Wirral addresses moved wholesale from L43 / L44 to CH43 / Ch44. Areas of largescale (re)development can also undergo changes to existing postcodes as rounds are reorganised. Royal Mail expose addresses and postcodes via their website as:-
STEP 1 - Go to the website above and see if you can find your address listed. I would search first with the postcode you have been given. If you cannot find it that way then try searching with your 'Street' name. Try both the name of the block of flats and the 'Street' off which they are accessed.
If you find your address, and its correct postcode, and it is the same as you quoted in your calls, then you are victim of the update cycle for that to reach the likes of ISP's and OpenReach's backend databases. Try going back and escalating the call telling them that it does appear in PAF and challenge them as to why they do not already have it.
STEP 2 - If you cannot find your address on the website above DON'T PANIC. Your address may already be in their database but just waiting for a now occupied flag to be set so it appears to members of the public. Follow the link on the right hand of the webpage to:-
What to do if your address isn't found
This will ask you to let them know with a stated aim to respond within 48 hours. If you prefer there are phone contact numbers on the lower left of the webpage, just watch out for the 51p per minute band.
Good luck and please report back on progress.
Oh and I do suspect that Google Maps will be using a product called Code-Point Open. This is one of Ordnance Survey's free to use OS OpenData family of products. Whilst useful this is only updated Quarterly – February, May, August and November so may take some time to reflect a recently allocated postcode.
Edit - Just checked and OpenReach delivered an uplift to its External Information Points (EIP) in November 2014. See Here
This included the use of the Unique Property Reference Number (UPRN) from the LA's LLPG delivered via the efforts of GeoPlace as an Ordnance Survey product called AddressBase Premium
If you cannot find your address on the website above check with your Local Authority SNN Officer / Address Custodian to make sure they know the property is occupied. They send regular, sometimes daily, Change Only Updates (COU) to GeoPlace hence into Address Base Premium hence into OpenReach.
Edited by briansaab (Fri 13-Mar-15 00:55:31)