Hi,
HikaShop only sends an email notification when the order is created and then when the order is confirmed automatically by the payment plugin.
There is no "order pending" email in HikaShop.
Now, if the payment plugin asks HikaShop to send the email it sends when the order is confirmed also when the payment is pending, then I could see it happening. But in that case, what you want to change is the payment plugin and I don't remember any payment plugin we developed on our end doing what you're describing.
Which payment plugin are you using ? That would be the first thing I would ask here.