The double swing is a very effective melee technique. It takes a long time to get used to and is difficult to block. Usually players with more agility are capable of doing it while players with higher strength cannot. To avoid the double swing you have several options a kick, another block, chamber, jump away and swing, s key, etc.
The double swing is not bull shit, it's often used in Native and various other mods. It sucks for you especially, since you have around 80-100 ping but you can still learn how to fight effectively.