The general ruling about bank promotions is that they are associated with interest or suspicion of it, making their usage questionable. However, personal circumstances play a significant role in determining permissibility.
If you are facing financial hardship and cannot meet your basic needs, using the promotional money to pay rent is permissible. If your financial situation is stable and your basic needs are covered, it is better to avoid using this money. In cases of exorbitant rent increases, it is advisable to explore legal solutions to address the unfairness.