One of their customers, most likely not them, is trying to access your system. Keep that firewall up & running. Happens ALL the time. Send them all the techie data identified by your firewall and maybe you can just help put the low-lifes outta biz!
I'm surprised you've never experienced this before. Just put up a firewall? or a new one? Most allow you to turn off the notifications but still maintain a log of all activity. Check it out, you may learn more than you ever wanted to know!