My landlord didn't give 90 days' notice of the increase. Do I have to pay it?

No. Under Article 14, the landlord must notify you of any rent increase at least 90 days before the contract expires, in writing (notary, registered mail, or Dubai REST app). Miss that deadline, even by a day, and the contract renews on the same rent and terms. A verbal mention or a renewal offer sent late does not count.