As i aware of there are some case something like this, c't remember that full case but almost like an example below:

1) Development launch on Jan 2017 with 24 months construction period, i.e. Jan 2019
2) Marketing brochure stated the targeted completion date is xx Jan 2019
3) U signed SPA year Jan 2018
4) Developer say the SPA period is from Jan 2018 + 24 months, which is Jan 2020
5) So if they deliver the parcel anything between Jan 2019 - Jan 2020 still within the allowable period.

Conditions:
a) You have a copy of that marketing brochure
b) the marketing staff did told u that tentatively the project will be complete on Jan 2019

Based on this, u can go to tribunal whereby
"at the point when u want to purchase the property, u knowing that the project is going to be completed on Jan 2019 and brochure said that."
As a result, ur completion date will be Jan 2019 instead of Jan 2020 (24 months from ur SPA date)

So, anything can be challenge, so pls keep all materials in regard to the property u purchased in case u need to file against developer.

With that, i believe u can file to tribunal, by showing ur brochure and whatsapp msg (printed out).
IF possible, get a lawyer/expect to assist u on the content of the filing.