In particular, I'm looking for the story, where rishi Durvasa cursed mother Saraswati, because he couldn't pronounce something that lord brahma had taught him and mother Saraswati laughed at him when he was in brahma loka. I was also looking for the source for the story of which I only remember little since I had seen it somewhere years ago.
The episode of Saraswati Devi incarnating as Ubhaya Bharati has been mentioned in Sankara Digvijaya: The Traditional Life of Sri Sankaracharya by Madhava Vidyaranya
According to it, Saraswati Devi laughed at the Durvasa after hearing his out of tune utterance of Vedic mantras. Durvasa then cursed Saraswati due to her misdeed and out of leniency, showed her a way to get free from it. As a result, she took birth as Ubhaya Bharati.
To become the wife of Mandana in future, Saraswati was born on earth as Bharati (later known as Ubhaya-Bharati) under the influence of a curse for a misdeed of hers. It is said that in the assembly of Brahma, the sages were once chanting the Veda when the choleric sage Durvasas, who also happened to be in the company of the chanters, uttered the Vedic Mantras out of tune. Saraswati, the consort of Brahma and the goddess of learning, thereupon laughed at the sage, who was roused to great wrath by this insult. Looking fiercely at Saraswati, he cursed her to be born on earth as a human being. The Goddess in deep distress fell weeping at the feet of the sage and pleaded for mercy. At this plea of the Goddess, supplemented by the request of all the other sages to view the mistake leniently as the transgression of a daughter, the sage said to Saraswati: "You shall be free from the curse when you happen to meet God Siva in his incarnation as the Sannyasin Sankara." The stroke of destiny being irrevocable, she was born on earth in a Brahmana family on the bank of the Sona and grew to be the centre of all virtues and all learning. Astonishing all, she acquired even in her girlhood mastery of all the Vedas and the Sastras as also of all other branches of learning.