empty / ghost orders about 10 a day

-- HikaShop version -- : 3.2.1
-- Joomla version -- : 3.8.3
-- PHP version -- : 7.1.11
-- Browser(s) name and version -- : IE 11

We changed from VirtueMarket to Hikashop over christmas and are live now with Hikashop. We receive empty/ghost orders about 10x a day, sometimes every 12 minutes, sometimes not every day. The mail contains a few fields which are empty, but not all. All these orders have status cancelled. They are also stored in the back office, but there is no new customers from this order in the customers list. We checked the users: no other users than ourselves are registered. We installed Googles Re-capcha. All unnecessary emails are turned off, even the cancelled email is turned off. We do receive valid orders from real customers as well and I am pretty sure the ghost orders are not real customers which start and then cancels an order. We also never had this with VirtueMarket. Does anyone have an idea how to solve this ?

Good point; I could not find any post about this on any forum either. In the meantime I found out that the IP adress from which this cancelled orders are send belongs to our payment provider from which we use a plugin. I contacted them because to me it looks like their system is sending out some sort of cancelling message. They are looking at the situation.