I think the HDB service officer may have given you a wrong info. As a usual practise from contractors to HDB, once the first blk is completed, they will check and hand over the keys to HDB, not when all r completed. this is why in any hdb project, u see different batches of key collections. u will get a letter first to submit for application of HLE again... this to to check on ur income status to grant you the loan after the 2nd 5% d/p.
after which in about a month u will receive another letter to ask you to collect key. dun check with the main enquiry line. did u check with your customer service manager in charge of your project?