Landlord's right to increase rent if there is no proper lease contract

Good day,

I recently shifted to a furnished studio on 1st Aug 20. The building does not have contact information for any real estate or landlord. Sitting at their reception every time is just the usual 3 people.

I signed a piece of paper which is kind of a contract, gave the security deposit and advanced payment. The person did not give any receipt for this transaction.

I have now been paying for 2 months of rent on every 1st but they did not issue any receipt for these transactions. Now, on 4th Oct 20, they knocked on my door and told me that from next month they will increase rent for additional AED 200.

I want to know the law applicable to my situation because I think it's illegal increasing a monthly rent out of their "personal interest" and not providing receipts to their tenants. I think we are being scammed. Please help.

Thank you.