aws billing support case

I am a student currently learning AWS and recently encountered unexpected EC2 charges after accidentally leaving a GPU instance running. I have already terminated the instance and deleted all associated resources to prevent further charges. I also raised a billing support case, but it has been over 48 hours and the case is still unassigned or receiving automated responses. I understand the mistake was on my side, but I wanted to check if such delays are normal and if there is any way to ensure the case is reviewed. Any guidance would be appreciated.