Serious Question ??? I Need Answers!!

Okay Me And My Boyfriend Of 3 Years Broke Up In August Of Last Year And He Started Dating This Other Girl. They Broke Up In October And Me And Him Got Back Together In January When She Seen Me And Him Were Back Together She All Of A Sudden Popped Up Pregnant By Him. He Did Admit To Me That He Had Sex With The Girl But That Was In The Beginning Of October. Even She Doesn't Deny It. Now She Is Saying She's Seven Months Pregnant And Due On September 23rd. She Constantly Harasses Us, Blowing Up The Phone All Night. Making Posts About Me And Him On Facebook And Saying He's A Deadbeat. Blowing His Dads Phone Up. And Every time He Asks Her For A DNA Test She Always Claims That "Her Baby Is Good Without Him" She Is Really Pregnant That's Not The Issue Here. The Issue Is That She Is Claiming Its His And Causing All This Drama But The Times Don't Add Up And She Won't Take A DNA? Please Help We Have Been Dealing With This Since January.