The first thing I thought of whe I read this is what is Bowlingball.com's policy on this. Most websites I have ordered balls from say that you can request a certain pin position and top weight, but they do not guarantee to meet it. Again that is the chance you take buying equipment online without being able to see it/hold it before doing so.
If their website does not have such a disclaimer, then you have a right to be upset, if it does, then it is your fault for not reading everything before you purchased the ball. Neither here nor there now as it seems they are willing to give you a refund.
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Jorge300