Word or idiom to describe someone sabotaging something and then bragging from it not happening?

The generic word for sneaky sabotage is "undermining" or even "subversion".

But the scenario you're describing here is a little different. It sounds not just like sabotage, but a general type of manipulative tactic called "gaslighting": when someone secretly undermines you and then gloats and blames you for it. The pattern of behavior you describe includes all the indicators:

1. secretly rearranging/hiding your stuff
2. causing you to fail and then trying to convince you that it was your fault
3. harassing you (calling you non-stop at night) and pretending like it's normal and you're the rude one if you complain
4. trying to make you believe that they know more about your situation than you do ("I told you, you had no chance of winning")
5. when you fail as a result of all of the above, they deny doing anything and pin it all on you.

Basically, you're describing sabotage by gaslighting.

Here is a definition of gaslighting from PsychologyToday:

Gaslighting is a tactic in which a person or entity, in order to gain more power, makes a victim question their reality.

(https://www.psychologytoday.com/blog/here-there-and-everywhere/201701/11-signs-gaslighting-in-relationship)

It is not merely a clinical term--it has been in common usage since at least the mid-1990s. Here is an example of an article from 1995 which features the term: http://www.nytimes.com/1995/11/26/opinion/l-liberties-the-gaslight-strategy-066192.html

The Urban Dictionary of the word is pretty informative as well, with a good technical definition at the top, as well as some working descriptions from both a victim and an abuser of this tactic: http://www.urbandictionary.com/define.php?term=Gaslighting

Phrases that come to mind:

Throw a spanner in the works

https://www.collinsdictionary.com/dictionary/english/to-throw-a-spanner-in-the-works

A thorn in one’s side

http://www.dictionary.com/browse/thorn-in-one-s-side

You could also say that this person attempted to:

jeopardize your success

derail your success

thwart your plans to win

Such a person could be described as a schemer.

http://www.yourdictionary.com/schemer

snake in the grass (thefreedictionary.com)

One who feigns friendship with the intent to deceive.

A sneaky and despised person.

snake in the grass: A treacherous person, as in Ben secretly applied for the same job as his best friend; no one knew he was such a snake in the grass . This metaphor for treachery, alluding to a poisonous snake concealed in tall grass, was used in 37 b.c. by the Roman poet Virgil ( latet anguis in herba). It was first recorded in English in 1696 as the title of a book by Charles Leslie.

The German term Schadenfreude (there are umlauts in there somewhere) comes to mind.

It means taking pleasure in the misfortune of others as in "I told you he couldn't do it."

By adding some subversion in at the front end, Schadenfreude seems to come closest to meeting the need.