Can check with Strata Board , see whether can classify under latent defects " A patent defect is one that is detectable either at or before apparent practical completion or during the defects liability period. ... By contract, a latent defect is one which has been concealed in the works and may not become apparent for many years.

You can ask Contractor take out these rusty head screw and replace with a new stainless steel screw and patch back the falsed ceiling , or use screw driver to loose and exposed the screw head and apply " Rust Converter " on it and further apply some enamel paint on it again , wait for dry and screw back the screw deeper into the support frame ( but too deep ) , patch and paint the affected hole . The Stainless Steel screw on self taping type , use back the same screw is possible .

Can try the fish ball stick Department

SINGAPORE - A new Municipal Services Office will be set up to serve residents in a more seamless way.
It will get different agencies to work more closely together especially when responsibilities are split, Prime Minister Lee Hsien Loong said in his National Day Rally speech on Sunday night.
The new office aims to resolve the problem of residents getting frustrated when their complaints or requests bounce back and forth between several agencies.
It will be housed in the Ministry of National Development (MND) and Minister in the Prime Minister's Office Grace Fu will oversee it, Mr Lee added.

忘记一个部门，Controller of Housing , under URA, 这个是开發商监管部门，可以试一试，外面也有些替人 做 Claim 的，但是要花錢。Redas , 是一个公会，自己人管自己人，不知结果如何？