If you hit up Bing ads support then I am sure they should be able to help you out. Also, there are a lot of IM forums that have services selling Bing ads coupons for a small fee.
for $5 - 1 Coupon code of $100 Expiry of Code : 30th June 2018 https://zeerk.com/jobs/online-marketing-seo/i-will-provide-you-100-bingads-coupon-code/