The first two lines are not second person plural.
They are absolute ablatives (one for each line) and therefore "impersonal".
The first line has confutare (silence) and maledictus (cursed) and reads roughly "When the cursed ones are silenced".
The second line also has implicitly maledictis and the other part of the absolute ablative is the participle addictus (devoted).
The target of the devotion is expressed with the dative flammis acribus.
The only verb in a personal form is the imperative of the third line.
I would translate the stanza like this:
When the cursed ones are silenced
and devoted to the piercing flames,
call me with the blessed ones.
The choices of words may or may not be optimal, but I hope the grammatical structure is conveyed clearly enough.
There are four ablatives (confutatis, maledictis, addictis, benedictis), two datives (flammis, acribus) and one accusative (me) in the stanza.
The participle confutatis does indeed look like the present active indicative second person plural, but context indicates that it is an ablative of the perfect participle instead.
These two forms differ in the length if the last i which is typically not indicated in writing.
(I'm not sure if the distinction was made when those lines were first written.)
For the verb addicere the same forms are different: the personal form is addicitis and the participle is addictis.