Hi Mick
According to Netflix's help centre "If you are currently billed by Google Play, you must add a new method of payment on netflix.com/youraccount to continue your membership" so there is a good chance the emails are genuine. Even so, to be safe don't follow any links in the emails but log into your Netflix account and use the drop-down at the top right. I may well be teaching granny to suck eggs here, but better safe than sorry 
It is all too easy to spoof an email "from" address and to create a false link like this http://www.netflix.com/anaccount. (Link goes to Wikipedia article). I get particularly annoyed at emails from my bank regarding internet security that contain links for further information!!!
Brian G