Sure you can do it. It's not that important how good your memory is, but how much time you spend learning and how focused you are.
For Thai, in my opinion:
Get some classes with a teacher (not just a native speaker. A teacher will be able to teach you right pronunciation. My suggestion is this:
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(they have a youtube channel about learning Thai).
Subscribe to Pimsleur- great for beginners (but don't start with only this)
The best book to teach you writing I think is Write in Thai in 4 weeks, just obviously you won't learn it in 4 months even, but you can understand the most important things. It is not that difficult in general.
Just don't listen to people who would tell you that you will learn Thai the best on Sukhumvit in a bar or when sleeping. Those people just look for excuses.
Also Pamboon Thai for beginners is good although a bit old fashioned, as you can listen to the dialogues that are in the book.
Do you have any confirmation on paper or in messages that you paid the deposit? You need a proof that you rented that house and that you paid the deposit if you havent signed any contract.
you are right. I missed the information about the contract. Then its a lot worse situation and I would tell the owner to immediately provide all the documets as Im going to report to the immigration where Im staying or to give me back the deposit and move out (both options are unlikely to happen) and after he refuses, I would go to the immigration to ask them what to do. All what Ive said now may finally resolve the problem but the chances are like
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to resolve it on time.
So summing up: you need to find another place as quickly as possible.
To talk with the owner it would be the best to ask a Thai person to do the talking.
I had a similar situation. I went to the immigration normally to do a 90 day report. They told me to pay the fine for the owner (1500baht), and they called him. They told me that he needs to cover the cost and if not, to come back and tell them he refused. The owner sent me back the money the next day. But I dont know what would happen if he didnt do so.