While I understand why you’re annoyed, are you sure you want to cut off communications?

In the middle of a pandemic, it makes sense that the CEO will have had a pretty unpredictable schedule, and I can see them having to prioritise a LOT of other things over a possible new hire. Speaking as a business owner, it’s been a very crazy time. The fact they went out of their way to make contact in the first place is a pretty big deal, and shows they value you.

I would also say it’s unwise to cut off industry ties without a good reason. If you have something else lined up, fair enough. If not, hold your horses! You’ve got nothing to lose by waiting. There’s nothing to stop you applying for other positions in the interim. Also, the post covid job market (especially for grads with little experience) is going to be competitive and tough. Food for thought.

If you really are set on having nothing further to do with the company, then politely decline any further invitations to talk when they next contact you. Something along the lines of “Thank you for the opportunity, however I have since decided to pursue other options.” etc