There is an interesting difference between the way in which Satan refers to God and the way in which Beelzebub, his second-in-command refers to God. Let us look at the beginning of their conversation to show this. Satan opens refering to God as "the potent Victor in his rage" and then only goes on to refer to him as "him," refusing to name him or give him the respect that it his due. Note the following example:
To bow and sue for grace
With suppliant knee, and deify his power
Who from the terror of this arm so late
Doubted his empire, that were low indeed...
It is as if Satan continues in his rejection of God after the failure of his rebellion. He refuses to acknowledge the power and authority that God has and has amply demonstrated through his victory over Satan.
However, by contrast, Beelzebub clearly seems to recognise the authority of God, as he refers to God as being "Heave'n's perpetual King" and tells his "Prince" that God has shown himself to be supreme through his victory:
But what if he our Conqueror, (whom I now
Of force believe Almighty, since no less
Than such could have o'erpow'red such force as ours)...
Beelzebub clearly regards God in a different way, that reflects his understanding of his new position and the way in which he and his fellow angels were vanquished by God's angels.