Is the written contract considered valid, or is it an injustice to the colleague? And is the colleague entitled to request the evacuation of the apartment or to change the rental value? And is he entitled to inform the office of a change in the agreement without my consent? And is it permissible to cancel the verbal agreement and abide by the written contract in the event of the colleague's dishonesty?

The contract is the law between the contracting parties, and it must be fulfilled unless it violates Islamic law. If the two apartments are rented together as one deal, and you both agreed on dividing the rent and you accepted the increase, then this agreement is binding on you for the agreed-upon period. After the first period ends, you have the right to leave the apartment or to agree on a new contract that suits you independently.

However, if each apartment is rented under a separate contract, and you rented your apartment for ten thousand, then this is the amount binding on you. Anything you added beyond that is considered a donation to your friend, and you are allowed to stop it and adhere to the original amount, because the contractual link is between you and the owner or their agent (the office). It is permissible to revoke a donation or gift before its possession according to the majority of scholars, and in some cases, even after.

It is advisable to maintain the relationship and mediate to resolve the dispute between you.