Http to Https Errors

Hi i have changed servers from Bluehost to SiteGround ( best move i ever made ) I had a SSL set up for one of my websites https://www.buckspartyvenues.com.au on Bluehost. I have setup SSL on all three of my sites on Siteground including https://www.buckspartyvenues.com.au

They are

https://buckspartyvenues.com.au
https://thecruisefactor.com.au
https://buckspartycruisesydney.com.au

The first one i think has issues with 2 SSL certificates one on Bluehost and one on Siteground.

They all have issues with mixed content.

I have tried WordPress HTTPS plugin but doesn’t seem to be working.

Any advise would be gratefully received. Dont want to re upload all my pictures and content again if i can help it.

This is the error from Why No Padlock

SSL verification issue (Possibly mis-matched URL or bad intermediate cert.). Details:
ERROR: no certificate subject alternative name matches

Thanks

Danny Kirk