Yes. The Quran commands returning trusts to their owners (4:58) and forbids betraying them (8:27). This includes money left with you, secrets, and the duties of a job. Delaying payment of a debt when you are able to pay is also a form of injustice.
Hiç şüphesiz Allah size, emanetleri ehline teslim etmenizi ve insanlar arasında hükmettiğiniz zaman adaletle hükmetmenizi emreder. Allah size ne güzel öğüt veriyor. Şüphesiz Allah işitir ve görür.
Ey inananlar! Allah'a ve Peygambere karşı hainlik etmeyin, size güvenilen şeylere bile bile hıyanet etmiş olursunuz.
This is general information, not a fatwa. For your own situation, ask a qualified scholar.
Questions about halal and haram
Is it haram to betray a trust?
Yes. The Quran commands returning trusts to their owners (4:58) and forbids betraying them (8:27). This includes money left with you, secrets, and the duties of a job. Delaying payment of a debt when you are able to pay is also a form of injustice.