And this is waht my hoster told me about my ssl problem.

The issue here is with unsecure content on your website:
jquery-1.12.4.js:5 Mixed Content: The page at ‘https://pro-deal.nl/onderhoud/’ was loaded over HTTPS, but requested an insecure image ‘http://dummy.xtemos.com/woodmart/demos/wp-content/uploads/sites/2/2017/06/wood-meint-2-bg.jpg?id=673’. This content should also be served over HTTPS.