[Stripe] Multiple stripe customers created.

[satyakam-nividata]

In stripe, multiple stripe customers are created. It creates a stripe customer per order. It should create only one stripe customer. If we use an existing card, then it works perfectly. But when you use a new card, it keeps creating a new customer for each order.

@damianlegawiec also when you use same card details as new card, it creates another entry in Stripe.