How much wear is there on the chain? ie. Did you check it with a chain wear indicator like
this? If you did was it at 1% or 0.75%? If it was at 1% how long has it been at that? Is this the 1st new chain on your cassette?
I know there are a lot of questions here but If it was showing 0.75% and had only just got the that measurement and this is your 1st replacement chain then you probably don't need a new cassette. Usually I reckon on 3 replacement chains for 1 cassette/freewheel.