SimCity Social and the missing Diamond deal - scam much?

When you select the Pay by Mobile option, on SimCity Social (a Facebook game), the cheapest deal now offers 10 Diamonds for €2,50. However, when you select it and click on to make the purchase, you're actually getting either 9 Diamonds for €2,50 or 12 Diamonds for €3,50 - see the next screenshot, below;