My manager didn't sent me a notice that the amount i paid for rent last month was $70 short?

Okay, so i somehow ended up miscalculating and my rent was $70 short. I had no idea about it. There is a %10 late charge fee. My manager did not send me a notice or an email to tell me that i owed that money and now the late fee has built up to $300! The way i found out is when i signed up for online payment and i ntoced that negative balance of 300. If i hadn't signed up for online rent payment, i would never have known that i owed them money and the late fee charge would have built up! Isn't it their responsibility to send me a notice at least?

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