in some earlier posts on this thread about the number of cases where the father is not the biological father of the child there were extraordinary numbers quoted.

It is around 1.8% in new Zealand and likely to be close to that in many countries -  amuch lower percenatge than other quoted but still a fairly large number when you count them in groups eg children currently 0-15.

Under some circumstances fathers who find out are entitled to refunds of child support/custody payments.

https://www.stuff.co.nz/life-style/parenting/93634977/Sex-lies-and-a-baby-When-dads-discover-they-aren-t-the-father-after-all