Double bill gone wrong

I was happy with the app and decided to pay for premium because they offered a great price of $49.99 for the year. A week later I got an email I would be billed again at full price: $79.99. I asked support about why there were two subscriptions. In their infinite wisdom, support decided to cancel my account, delete the promotional price, and tell me I need to pay full price of $79.99. Wow. That's the worst possible way to handle that situation.