Solve a mystery

1t
2J
3n

The above are 3 text messages which I got last night/this morning at 12:01 from "Unknown. They all arrived within about a half second, in numerical order.

Even stranger, when I actually open the texts, the letters aren't there, only the numbers.
There is no way to reply to the texts, not that I would anyway.

Does anyone have a clue what this might be, or has anyone ever gotten something like this?

.