Unfair treatment that lead me quit my job

I have been working for Nedbank client services for 6 years cause of covid we moved to different departments I than moved to merchants help desk for 2 years i was not copping i was in and out of hospital because off depression my doctor even wrote a referral letter but I was told by my manager that I am not taking my work serious even after telling them that I atleast need training because I wasn't copping at all 2021 June I had to quit my job because I felt that I'm not being taken serious and I was told that I owe the bank as I was on maternity leave and now all the 8 years I have been working for just went down the drain and I have to pay the bank an amount of R55000