Is the dismissal legal?

Good morning. Please tell me what to do. I am a mother of three children, I was on maternity leave to take care of a child up to 6 years old, in March of last year we were forced to go abroad. When the child turned 6, the next day I was dismissed for absenteeism. There was no warning. At that time I was abroad. Are their actions legal and what should I do next? I found out about this when I picked up my work permit, the record was already there.