Taylor Swift on Sunday lamented the sale of her catalogue to the manager and mogul Scooter Braun, writing in a scathing Tumblr post that she was sad and grossed out that her music now belongs to a man she accuses of subjecting her to years of incessant and manipulative bullying.

“This is my worst case scenario,” Swift wrote, in a post that made reference to clashes with Kim Kardashian and Kanye West.

Braun’s Ithaca Holdings announced on Sunday that it is acquiring Big Machine Label Group, which released all of Swift’s studio albums and owns her masters. Swift said she learned of the sale the same day.

Swift left Big Machine and signed with Universal in November because, she said, she knew that re-signing with the group that had managed her since she was 15 would only result in her not owning her future work.

“When I left my masters in [Big Machine Label Group founder Scott Borchetta’s] hands, I made peace with the fact that eventually he would sell them,” she wrote. “Never in my worst nightmares did I imagine the buyer would be Scooter.”

Braun, she alleged, got two clients including Justin Bieber to bully her online about a leaked and illegally recorded snippet of a phone call with Kardashian. She also said West, a Braun client, organized a “revenge porn music video which strips my body naked”.

Braun, she said, has now “stripped her” of her life’s work, which she “wasn’t given an opportunity to buy”.

“My musical legacy is about to lie in the hands of someone who tried to dismantle it,” she writes.

Representatives for Braun and Borchetta did not respond to requests for comment.

Swift wrote that she was glad to be “signed to a label that believes I should own anything I create”. She also advocated for artist ownership of songs and hoped that the next generation of singers and songwriters will “read this and learn about how to better protect themselves in a negotiation”.

“I will always be proud of my past work,” she added, making sure to plug her new album, Lover, which will be released on 23 August.