I think that at this point in our relationship, we should stick to written communication (text, email, or physical) so there is a record to which we can refer in case of disagreement.
This doesn't accuse him and read neutrally implies that either of you may want to refer to the record. However, it makes the effective point that you require the record. If he does not read it neutrally, he may claim that you are calling him a liar. You can respond with something like
I'm not calling you a liar. I'm saying that this is a time for a consistent record to which we can both refer so as to minimize the chance of misunderstanding.
If he continues to rage, don't respond. Print the messages and store them in case they are needed in the future. I wouldn't read them more than to determine that there isn't actual information in them. Of course, this may not be a problem. It's only a possible response at this point.
I wouldn't mention the money, as it suggests that it is still an open issue. Stick purely to talking about the relationship in this advisement. The point is that you want the assumption to be that he will pay you the entirety of the damage deposit. He may want to make a partial or no payment.
Follow up by asking for an update on when you will get your damage deposit back, reminding him that you have pictures documenting the appearance of the room at the time of your departure. You may also want to remind him of the answers to any of his queries. Again, treat the amount of the money as set; the only question is when he will send it.
If you do agree to a reduced amount, tell him that you disagree that it is justified but that you are willing to agree to the reduced amount if paid by some specific date. That's not for IPS reasons but in case of a legal case later. The idea is that you are doing him a favor by agreeing to the reduced amount so as to bring the process to a close. Then if it goes to court, he can't say that you agreed as to damages of so much and then ask for additional relief.
You may want to start looking into options if he does not return the damage deposit within a reasonable time frame. Are you poor enough to get legal aid? Is there a regulator you can contact? Do you have to hire your own lawyer? Is there a legal provision that allows the lawyer to collect legal fees from the landlord rather than you?
I wouldn't bother threatening him with these options. Let the option that you choose do the threatening once you activate it. At most you might threaten him with the lawyer once, right before you retain the lawyer, something like "If I don't have a check for [amount] by [date], I'll refer this to my lawyer." You should already have talked to the lawyer and settled on fees by this point. It's basically a last ditch attempt to avoid paying the lawyer's retainer. With free options, there's no point. They have more experience and can make the consequences clearer.
Do not bluff. If he calls your bluff, you have no further recourse without doing the thing that you were bluffing. So if you say that you are calling a lawyer and don't receive the payment, call the lawyer. If you aren't willing to call the lawyer, don't threaten it. Just write off the money and move on. I'm assuming here that other options are not available. If one or more is, then you still shouldn't bluff. Just use the other option.
For legal reasons, try to keep emotion out of your communications. Stick to the facts. If you become angry, turn the case over to someone else to collect the money. That person won't have the same emotional investment.