Agency raising the rent, can we refuse?

I received a letter from the estate agency. They want to raise the rent by 4000¥ a month, which is around 5% of the initial price of the rent. (It’s the new new year wishes card I guess)

They already bumped the service charges by 1000¥ this year.

The letter contains a paper to sign and send back.

The thing is, though the place is great, a 4000¥ bump is too much and we plan to move out at the end of our contract in June.

Can we refuse this rent bump (to save 24000 yen) or do we have to swallow the pill and just sign the paper?

thank you!