I applied to an apartment without paying fees, now I want to cancel but they still want deposits

I was recently on the hunt for a new apartment. I was worried about some apartments going missing so I applied to more than one. Now I have moved into an apartment and signed a lease but one of the applications is giving me trouble.

The application in question was sent as an attachment to an email saying that the application fee, administration fee, and security deposit were due 72 hours after the application was received. After signing the application and emailing it back, I got an email taking me to a site where I could pay the fees. I hadn’t read the original email close enough and thought that the fees were due 72 hours after the application had been accepted.

I got no further correspondence for about a week, and forgot about the whole thing, when I got a phone call saying I had fees due. After some emails with an agent I learned that they had run my application without me paying the application fee and they were going to let me know whether or not I was accepted after I submitted all of the fees/deposits. I re-read the application that I signed and it only mentions the application fee. I went ahead and paid the application fee, but did not pay the remaining balance as I saw no reason to do so. I had not been made aware of any of the above information and it was not in the application. The two remaining fees (administration fee and security deposit) are still unpaid as I feel like I have no legal obligation to pay those fees.

When further questioned, the agent said that the fee is for holding an apartment. I never requested it be held and again, it was not written anywhere that submitting an application was the same as requesting a hold.

Do I need to pay the remaining fees or am I in the right here? Should I seek legal advice? The agent threatened me with attorneys if I do not pay the remaining balance (less than $300).

Edit: this is in Alabama, USA