Cancellation of SPA for delay in delivery and defaulting on payments

Hi

I bought an off-plan property from a developer in downtown during the peak time. My payment plan was based on construction with completion being Dec 2019. I have paid more than 50%.

I requested the developer to readjust my payment plan as the project is delayed. They moved on payment forward and sneakingly changed completion date to Aug 2021 in the document. The SPA still says Dec 2019.

Now I'm struggling to pay the next payment due to COVID-19 and project is completed 56% as par Dubai land department and 60% as per the developer. The developer is asking for payment and calling me every day.

My question is can I still use the delay in the project as a clause to cancel my unit?

Can I cancel my apartment and how much can the developer deduct?

After selling me, the developer started offering customers post-handover payment plans for 4 years, which is very unfair as even if I complete my payment, no one will buy from me as the developer is selling something with 4 years post-handover.

Can legal help be provided in this regard?