Such troubles in buying in-game currencies are inevitable.
But luckily, you can do something to control the situation.
#1 Although it is labeled optional, ALWAYS indicate your ACTIVE EMAIL ADDRESS. Xsolla will send an e-mail which will serve as a receipt to your successful transaction. This will help you provide certain informations that the Support team needs whenever you've experienced technical troubles while buying (eg., delayed rubies, etc.)
#2 ALWAYS have a trial-purchase whenever you see a newly added method of payment. The importance of doing this is to prevent the hassle of not receiving your rubies on time for an existing promo. For example, you bought 1 000 rubies under a new payment method and an error appeared that made you miss to participate on a promo. Having a trial-purchase of small amounts of rubies will let you know if the payment method is now working properly.