There could be a few reasons of why I will not reply, but it is best to note the most likely reasons. In all instances, if you are a scam, or SPAM, I will not reply. If you are hostel or vulgar, I will not reply. If you don’t leave a message, I can not reply.
For email, if you only write one or two sentences, I will not reply. If you are not going to put effort in writing, I am not going to entertain you by replying. It will be good to at least write one paragraph. If you are writing an email for the first time, and need recommendations on writing a good intro, consider sending an email to firstname.lastname@example.org. You can send a blank email, and this is an unmonitored auto-reply.
For Messaging or SMS, if all you going to do is write OK, or Yeah, then I will assume you lost interes in the message, and will lose interest in trying to keep the conversation going. If you wish to reach out to me via SMS, you can send a message to my [Cellular] Number. This is the most direct option in reaching out to me.
As for telephone calls, any of my publicized numbers should work. However, if my phone is in DND more, then you would go to voicemail. If you don’t leave a valid message, I can not return your call.