Learn Spanish (Latin America): Me transfieren a la extensión, pero nadie habla. - They transfer me to the extension, but nobody speaks.

In Spanish, you can use the third-person plural to describe an action without specifying who is doing it. This is called the impersonal "they." It works just like English when we say "They transferred my call," meaning an unspecified agent (like a system or an unknown employee) performed the action.

Is transferir a stem-changing verb?

Yes, transferir is an e-to-ie stem-changing verb. In the present tense, the e in the stem changes to ie in all forms except nosotros and vosotros, which gives us transfieren here instead of "transferen".

Why is there no no before habla if Spanish usually uses double negatives?

You only need a double negative if the verb comes first. Because the negative word nadie (nobody) is placed before the verb habla, the no is dropped. If you wanted to put nadie after the verb, you would need the double negative: no habla nadie.

Could I use para instead of a here, since we are being sent to a destination?