"Unfortunately, at the time I ran everything on Instagram, so when that was gone, that was the whole business gone," she told BBC Radio 5 Live.
At least half of micro businesses - companies with fewer than nine employees - in the UK are victims of cyber-attacks every year, compared to just a third of other companies, according to the Association of Independent Professionals and the Self-Employed (IPSE).
Ms Kotomah, whose business Boresa Kotomah is based in London, had not studied fashion. She taught herself to sew and began designing clothes in 2018. Due to interest on Twitter in her fashion styles, she started an Instagram account and gained 5,000 followers in seven months, after a photo of a dress she made went viral.
Interested customers would send her a direct message on Instagram enquiring about prices, and commission her to make the dresses.
Ms Kotomah would invoice her customers using PayPal and mobile app Invoice2go, and her reputation grew by word of mouth and through shares of her outfits on Instagram and Twitter.
But then it all stuttered to a halt.
"I woke up one morning and my account was deleted. I received an email from Instagram saying I had violated some terms and I had done certain things that I know I didn't do," she said.
"My business at that time was my livelihood. That was what I was doing full-time. I'm self-employed. So if I'm not making money from working, I'm not making money at all so I was just thinking like, 'What am I going to do?'"
Ms Kotomah's designs have been worn by actors, influencers, singers, models and dancers.
Ms Kotomah was so disheartened that she stopped designing for two months and considered other jobs. But then she decided to give it one more try. She started a new Instagram account, learned more about running a business, and set up a website showcasing her work that offered ready-to-wear clothing available for immediate purchase.