Background image is not responsive AGAIN!

Hi guys, as it happened to someone else in the past, I found out that the background of my website is not responsive with smartphones (i.e. iPhone 5)
This is it:
http://www.marketing-branding.cl/

I tried with the codes that Hardeep Asrani and gouravwptech posted in this thread (https://wordpress.org/support/topic/background-image-is-not-responsive?replies=22)
but nothing helped it.

Instead of a normal presentation, you’ll see that if you scroll down the image is overlapped plus other errors.

Please help me to fix this issue.
WordPress version is 4.4.2, and the theme version is the newest one (1.8.4.0)