My man says he was banded?

he wasn't snipped. But i am now 7 weeks pregnant. He is going to assume i was cheating but i wasn't. Do you know of any articles i can look up to prove to him that because he wasn't snipped but just banded that he did indeed father our baby? I had my last period may 7th and my conception date they said was around the 22. me and my man were "together" the 23. so that would mean its his. but i know hes not going to believe me. My grandma is a nurse 40+ years and has said that during her nursing career she took care of many women who were pregnant to men who were banded and that method fails often and no respectable doctor uses that anymore. I just don't know how to tell him because i know what he's going to assume. that's why i want to find information to print off and show him. I love him more than anything and i just hope he realizes i didn't cheat. Also, I had been told by 2 different doctors that i couldn't ever have kids so he should see that doctors aren't always right.