My ex thinks I'm stalking him. How can I convince him that I'm not?

My ex and I broke up 8 months ago and we haven't spoken together since then. I sent him a happy birthday message 7 months ago and he blanked me so I decided not to write to him anymore.

The other day my friend (who is mutual friends with him) told me that my ex said I should stop sending people I know to the events that he was at. Apparently my ex had bumped into a guy who was half Spanish and half English at the event (I'm half Spanish/English too) and had thought that I had sent him there to spy on him. The thing is I don't even know who this person is nor do I know where my ex goes (and I don't even care) Why would my ex accuse me of sending people to the event he goes to just because we share the same background?
My ex thinks I'm stalking him. How can I convince him that I'm not?
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