Her son explained that he and some other Kenyan men had been given two weeks of combat training - and he was heading to the battle zone in Ukraine, which Russia invaded in 2022.
Within days, he told her that he and others had been ambushed in an area controlled by Russian forces. She pleaded with him to come home.
"I said: 'David, please leave that place.' He told me: 'How can I leave? I signed a contract. Give me at least one year.'
"Then I received the message I feared," Mrs Kuloba said.
It was 4 October. David had sent her a voice note saying he was about to go into battle and in case he did not survive, he wanted her to have details of his Russian military ID and contract, which was written in Russian.
He urged her to take the documents to the Russian embassy if anything happened to him.
That was the last time she heard from him.
Confused and terrified, she sought help not long after from her son's friend, who told her that he had heard David was dead.
"I asked his friend: 'How do you know?' He said: 'Let me give you the number of the agent who received us in Russia.'"
Mrs Kuloba messaged the number - the replies came in Russian at first. When she identified herself, the person told her in English that David was missing, feared dead.
"I'm sorry to tell you this about your son," the agent said.
