I've been threatened and frankly I'm scared

So on Friday, February 22nd, I was playing ARAM with a close friend. The link to the game is attached to this post. I was playing Nami, and my Illaoi walked into the enemy Vel'Koz's spells and died. I got really mad because my teammates were getting hit by a lot of poke and I couldn't do anything about it due to ARAM's healing reduction on allies. I yelled at them for inting and called them pathetic. That was uncalled for and rude. However, what actually set me off was the Illaoi player's reaction to this flaming; they justified it by saying that he needed a null-magic mantle to counter their poke, as they had no magic resist. I couldn't fathom inting for a 450 gold item after I survived long enough to buy Athene's and a Deathcap after my first death (I started with a fiendish codex). After a few exchanges of rude language, and them calling me a child, I muted them, deciding that I wasn't helping myself, and I wasn't helping them. It felt immature to continually reply to them, and I don't regret doing so. After the game, he added me so he could type "Ults then runs away" about 15 times, including in reply to me several times, and 8 times after I loaded into my next game with my friend. After continuing to talk to them (I realize that in retrospect, I should have blocked them and never accepted that friend request) they insulted me over and over. I once again was told that I was a child, that I was a 110 lb puny kid (I wasn't genuinely upset by that, but I am very self-conscious of my weight). The Illaoi player saw me telling our Caitlyn that she shouldn't ult the tank in front of her (literally point blank, no exaggeration), and instead, she should use her auto attacks, as she had a Rapid FireCannon, an Infinity Edge, and a Phantom Dancer; they thought I was a try-hard 16-year-old who just watches professional players all day, "sucking them off". This brings me to the important part of this post: in response to my rather scummy behavior (I won't refute it, I was rude and mean-spirited today), they said that they were going to look up my personal information via my IP Address, and steal my login information so that I would have to "start over, because [I] was rude." I replied that this is a "literal crime," since stealing my personal information via my IP seems incredibly far from what I would consider a legal activity. This in conjunction with my credit card info being on my account, I was very startled. They said that: it isn't illegal, "it's a bug I found" and that I should read the law. Then they told me that they were going to block me until they wanted to harass me again. As soon as the game ended, I tried to copy the chat log, but they blocked me before I could. I immediately changed my password, but I'm still partly scared that there's a way for this person to steal the account that I've owned since March of 2015. Is there anything more I should do to ensure the security of my account?

TL;DR : I flamed someone in an ARAM game, and after adding me and talking for a while, they threatened that they would steal my account info as punishment for being rude to them.