でたらめじゃなかったです
出鱈目じゃなかったです
detaramejanakattadesu

Noun
Desu Copula
na-Adjective

The polite, past negative form of でたらめ

1. Wasn't nonsense.; Wasn't arbitrary.; Wasn't made up.

Past/Perfective
Negative
Polite
Casual Register
Usually Written in Kana