After buying a problematic power bank

Can someone explain this to me…..i bought this power bank 4days ago….it was working fine then suddenly it stops working…..i took it back to the seller telling him….i thought he would change it or myb ask me to pay half of the amount for a new one…but nope…..this man litterally starts using abusive words telling me I’m at fault….saying I’m the one who spoilt it

I was so confused I’m trying to calm him down…….buh he keep raising is voice ive to shift at the side …few people came asking me what happened I explain and they all asked him to give me another one
After the conclusion he did give me another one but the scariest part is
He said i shaa see…i was so scared cause idk what he would do to me….idk if am wrong buh i explained to my sen brr tellinh him i will need to return the power bank to the man cause am scared Nd dont know what the words he said meant