stop numbers being shared between phones

[#1]

We have two Plusnet SIMs, one in my husband's phone & one in mine. Account & bills in my name. Problem is my husband's phone contacts keep showing up on my phone (but not vice-versa). Both phones Samsung. I've deleted numbers a couple of times but they keep reappearing. How can I stop this? Thanks, Ann

[#2]

@AnnF 

I doubt this is anything to do with the Plusnet SIMs but rather to do with the Android operating systems on the phones and the associated Google accounts.

Did both phones got the same google account entered when they were originally activated or since? If so then change your phone to another google account.

[#3]

Welcome to the Forum

Edit       jgb beat me to it 

Just a thought are the contacts saved on the phone or Google quite a lot of phones now save the contacts to Google if you don't tick a box

Why are my contacts saved to Google?

Android is heavily tied to Google accounts, and in most cases, your phone's contacts should be backed up to Google Contacts already. You can verify this by opening Settings and heading to System > Backup. Make sure that backing up to Google Drive is enabled and check that Contacts have been backed up recently.

[#4]

 I have two iPhones linked to a single Apple account These phones are on different mobile networks. These behave in exactly the same way.

Presumably Google gave something similar for Android.