Your firewall is properly blocking it, there is nothing to be concerned about. The attacker isn't going to get anywhere.
You can see the owner of the netblock sending these IKE requests here:
https://wq.apnic.net/static/search.html?query=164.52.36.247
I suppose you could try contacting the abuse email for that netblock, but in my experience with the specific country involved here you are just wasting your time. It could also just be some kind of misconfiguration on their end but I highly doubt it.
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