We have been getting a spam of 10-15 failed orders several times a week within about 15 minutes of each other.
It started a month or 2 ago.
The addresses are usually one of several that are repeated each time this occurs. Unfortunately the data from previous failed orders disappears so I dont have the old spam orders.
Are these SPAM orders actually causing a problem? If not then they will be cleaned up automatically by the setting to delete uncompleted orders. I know it's a pain but at times there are kiddies that just do this kind of thing, and attempts to block this kind of activity would likely end up blocking legitimate customers. Try blocking the IP a couple more times and see if they get bored and move on.