I struggle with a lot of disturbing thoughts. Personally I don't believe it is possible to shut these off. And everything I have read (which admittedly isn't a ton, but still...) pretty-much supports this notion. All trying to block intrusive thoughts does is to make them keep coming back stronger & more frequently. Here are links to some articles from PsychCentral's archives on the subject of how to deal with rumination. Perhaps some of the information in these articles will be of some help:

https://psychcentral.com/blog/5-mind...or-rumination/

https://blogs.psychcentral.com/dbt/2...sive-thoughts/

https://psychcentral.com/blog/8-tips...op-ruminating/

https://psychcentral.com/blog/the-re...uce-the-cycle/

https://psychcentral.com/lib/when-ru...mes-a-problem/

https://psychcentral.com/blog/why-ru...d-how-to-stop/

In my case, however, the technique I find most beneficial is one that is referred to as "compassionate abiding". Here's a link to a description of the practice:

https://mindsetdoc.wordpress.com/201...e-abiding-101/

May it be of benefit...