As @michael indicated if your origin IP ends in .59 it’s 100% not Cloudflare. When I curl directly to the origin server bypassing Cloudflare it returns the text/html content type that @sdayman indicated was the issue. So that would certainly seem to be an issue on the origin server. I’ve included the redacted output of my test below which I believe shows it is an origin issue. If your host believes it is still a Cloudflare issue, perhaps they would be so kind as to share their evidence to support that.
curl -Ik https://www.dotnikstudio.com/digital-product-design-and-development-services --resolve www.dotnikstudio.com:443:your.ip.address.59
cache-control: public, max-age=604800
expires: Fri, 24 May 2019 04:29:11 GMT
last-modified: Fri, 15 Feb 2019 17:41:47 GMT
date: Fri, 17 May 2019 04:29:11 GMT
alt-svc: quic=":443"; ma=2592000; v=“35,39,43,44”
Note Cloudflare is not listed in those headers demonstrating the request didn’t go through Cloudflare but the content type is still text/plain which is incorrect.