Prime voucher value not showing any more

I had added prime voucher to my account which was showing up when i had added. I happened to check for the voucher value few days ago and it showed zero. I got no communication about any expiry date and in fact the coupon was added only 5 months ago. It was difficult to reach a human in customer care but when i finally could, i was transferred to different people/team 5-6 times and finally they told this issue can be resolved only through phone customer care. When i finally navigated to the option of getting a call back, the call was not helpful and they did not know what to do. They just said we will get back. Now are there any ways to escalate this issue.