Habitual activities or repeated events do not take le了.
Yǐqián tā měitiān zǎoshang dōu xué (x) Yīngwén. 以前他每天早上都学英文。 Before he used to study English every morning.
Qùnián wǒ chángcháng qū (x) Běihǎi gōngyuán. 去年我常常去北海公园。 Last year I often went to Beihai Park.
Yǐqián yīnwèi tā hěn pàng, suǒyǐ dàjiā dōu jiào (x) tā 'Xiǎo Pàngzi'. 以前因为他很胖,所以大家都叫他小胖子。 Before because he was fat, everyone called him 'Little Fatty'.