ANNUAL INVOICE

My application for CHSO was approved now I must pay the annual invoice but I have been struggling . Been contacting the finance department since May and the letter is only valid for 3 months. The person they referred me has just been ignoring my emails and the invoice still hasn’t been uploaded on my profile . Whose fault will it be when the approval letter expires because I made numerous calls and sent emails and they would just promise to send the invoice .