Rashi: You will not be exiled to your neighbors, like until now, that you were exiled in the hands of Malchei Aram and they did not take you to distant lands, only until Damesek. Now I will hand you over to Sancheriv, and he will exile you to a distant place. Radak - the 10 tribes were exiled to Chalach and Chavor, far from Damesek. It mentions Damesek, for Melech Damesek harmed Yisrael greatly, like is written.

Malbim: I explained above (refer to 3:12:6:6) that first he exiled some of them to Damesek. This was not so harsh in their eyes, for it was close to their border. In the days of Yaravam ben Yo'ash it was in the border of Yisrael (Melachim II, 15:28). He prophesized that afterwards they will be exiled from Damesek to Chalach and Chavor.

Radak: He is G-d of legions above and below. Those that you serve are His messengers.