@Susan Thomas Good for you for being proactive and seeing there is a business that is run poorly, and searching for the right way for you to run yours.
There will be a state statute that sets out how he returns your deposit. In MO an LL has 30 days to return the deposit, or a combination of partial deposit and list of itemized damages. Google landlord tenant law in your state (assume PA?) and look for a government link.
If your LL does not comply with the laws, or does not return your deposit you could sue and place the responsibility on him/her to prove that any damage was not normal wear and tear, but no doubt you would have kept all records (maybe photos, too?) of your attempts to return the property to rent ready condition, and then you would have an argument in court.
2 things to note are that the LL (MO) only needs to mail the refund to the tenant's last known address, so did you provide your forwarding address? And if the LL wrongfully holds any or all of the SD, he or she is liable for 2 times the SD.
I think shame on that LL for for not responding to your requests; this gives LLs a bad name. BTW, asking you to write a letter stating what had been received in an email is preposterous. Sounds like he or she is trying to manipulate timeliness of correspondence on your part. I guarantee you, they won't show the email in court, only the letter.
Okay I just googled it, you have 30 days in PA to return an SD. You'll have to dig a little deeper, but there's the start. What mailing address did he or she have to use?
Good luck and report back.