Ummm why do frost dragons hit constant 200+ on me?

So, i recently got 86 dung and i was happy for frost dragons. So i get a cannon get anti-fires and go. I used karils top, veracs bottom, rapier, nezzy helm, glory, ardgone cape #3, zerker ring, barrows gloves and an anti fire shield. When i get their i drink the anti-fire and put on protect from magic and run out then set-up my cannon and start killing. I get combo'd a like 300 + 350 by a frost to kill me and i was like WTF how? My anti-fire pot was still good and my magic pray was up.

 

You were probably attacking while the Frost orb (swirling blue orb) was up which causes recoil damage. Just turn off auto-retaliate and walk away for a couple seconds.

 

yea i guess well gf my cannon zzzz