A DigitalPoint Forums thread links to a story named Microsoft adCenter can't bill correctly. It goes through how the individual used a $100 promo, ran up a bill of $111 or so and was billed the whole $111 instead of just the $11 (i.e. $100 minus the $100 promo).
December 21st - Spoke to a customer service rep (CSR) who thought that I had to pay the full $111.85, and then I'd get another account credit of $100. He really wasn't sure, however, so after arguing with him on how to read an invoice, I was finally transferred to a supervisor. The supervisor told me the same exact thing that the first CSR told me about paying the full $111.85 and not $11.85.
If you want a laugh, go read that post, kinda incredible.
Forum discussion at DigitalPoint Forums.

Comments:
tony scott
04/14/2007 01:06 pm
So what you end up paying.
Liz
05/08/2007 11:03 pm
I had a similar experience. I signed up for MSN Adcenter under a promotion, and was surprised when I was billed the full amount anyway. First, they said I never entered a promotion code - and that they didn't have any extra promotion codes to give me. (??) Ok... So finally I got an email through a newsletter talking about another MSN promotion. So I forwarded it to the customer service rep that was "helping me." The promotion was applied to my account and I ran some more ads. Same thing happened again. I as billed the full amount. They looked in my account and said there was a promotion in there, so I *shouldn't* have been charged. (They didn't offer to reimburse the amount that I shouldn't have been charged for) Then they assured me that the promotion would definitely be applied, and next time the ad credits would be taken out. (yeah, right...) I ended up just cancelling my account.
Vodafone Promotional Code
02/26/2011 06:55 am
I have signed up for Microsoft ad center but I could not see any deposit of 50$. Will it take time for the amount to get deposited or this happens immediately.
Zeolite
04/13/2011 08:49 pm
It can be very tricky to get it to work. I tried it from a link and only got $25. But at least that did work.