How to kill a destruction warlock as a frost mage?

I'm no PvPer, so while I've definitely been killed by frost mages as a warlock I couldn't tell you why. What I can do, though, is suggest some counter-measures for the problems you've brought up:

• You want to be killing the felhunter pet because that's who has the spell lock. Spell lock can't be used on instants. Alternatively, you might want to feint and start casting a fire or arcane spell, draw the spell lock onto the fire school, and then launch into your more powerful frost spells.
• When we warlocks are using Health Funnel to heal our pet, we're not casting and we're letting our health drain into our pet. Shift damage to the warlock.
• Conflagrate requires an Immolate to function, and Immolate requires a cast. If you get Immolate on you, you can bet that Conflagrate is coming, probably in the last few seconds of the Immolate. If you can break line of sight and let Immolate tick off, that will buy you precious few seconds.
• Remember Ice Block; if you can see your opponent casting Chaos Bolt, you can Ice Block to have them blow their cooldown, cast Ice Block again to jump out of it and use your biggest nukes. I believe it'll also make Immolate fall off.

He is right that tactic may work but I PVP quite a bit and I know as a DEST lock I would not waste the time to heal my pet I would just continue to cast on you or fear you. And a Dest lock will have a Glyph of Conflag which doesn't use up the Immolate. Just a couple of hints for you.

You should come to Zul'Jin and I will Duel you for Practice.

Aremis the Explorer