Missed call

So today I got about four missed calls in a row from a number I didn't recognize. I'll always refuse to answer to unknown or blocked callers, and I'll only call back if they leave me a voicemail.

By then I'd apparently really frustrated this person, and so they texted me. "Call me back."

So I asked who it was.

"Sienna."

And I told them I had no idea who Sienna was.

After a much-too-long pause (considering all other messages were sent almost immediately), 'Sienna' responded with, "Rong numba."

First of all, why did her grammar just change so drastically? And second, why do I feel like this should be the name of a dance?

Questions.