Earlier quoted context omitted.
I only communicate seriously
That's different from a "serious tone of voice" though. Think like the way a parent might start talking to their kid when they're angry but not yelling, with something like "You better get home right now." Or another example: "Call me" is a just a regular "let's chat about something", but "Call me." is "something bad happened I need to tell you about, so prepare yourself". Interestingly, you're actually partially doi…
For me and I guess most people I communicate with on e.g. Whatsapp. "Call me." is normal, expected, everything is fine, just need a phone call. "call me" is more like something has gone so horribly wrong (or someone is so incredibly pissed off) they've lost the ability to communicate normally. I wouldn't be offended, more like concerned.