Japanese by Example
Learning through examples in manga

Past decision still in effect with 〜ことになっている

ことになっている conveys that preceding action had been decided in the past and still remains in effect. It follows a verb in its plain form or a verb ending in ない.

Further reading

Examples

美少女戦士セーラームーン » Volume 5 » Page 235
ふだつきのキョーコちゃん » Volume 5 » Page 110
シャドーハウス » Volume 2 » Page 66