Generally, landlords have certain obligations to provide essential services, such as access to mailboxes, to tenants. If your lease explicitly states that you will receive two mail keys, and you haven't received them within a reasonable time, it could potentially be considered a breach of the lease agreement.
I would recommend keeping a record of all attempts to contact the landlord's office, including dates, times, and any responses received. Make sure to keep copies of any written communication related to the matter.
Next, write a formal letter or email to your landlord or property management company, outlining the problem and requesting immediate resolution. Be sure to include specific details such as the lease provision regarding mail keys and the amount of time that has passed since you moved in without receiving them. Also, include when and how you attempted to resolve the problem.