For 601K movement type documents you need to cancel with VL09 as these documents created once issued the goods to the customer.
Normal Goods receipt one (MIGO) use transaction MBST.
If you want to cancel those settled (Billed and accounting document cleared )check with Finance team are they able to correct anything from Finance side .If they insisted to cancel everything then you need to cancel Billing document ,Reversal PGI then do process again.