I feel your pain OP.
We live on the end of a row of three terraced houses and for the first two years endured our ndn slamming his front door every time he went in or out the house. He was nice, friendly etc and we got to know him a little, forgave his foibles etc. (I'm sure that he had stuff he endured from us too.) Then he died last year and his family were left to sort and sell the house, this took a few months and it was pure bliss - no noise. Unfortunately the house sold recently and we have had to endure builders noise etc since, then new neighbours.
The new neighbours have loud bbqs out the back, play loud (foreign, so we can't even understand it) music, just generally talk loudly out the back and front, slam internal doors all the time and slam the front door with every use. They have three cars and there are only 7 parking bays for the whole estate so keep stealing 'our' space
and when they can't fit a car out the front they park around the back. This is normally when they come in from a shift at work that must finish around one or two am and at 1.30 or 2.30am, depending on shift, park out the back and come in the back door, slamming that too. Invariably waking me up, their door being just the other side of the fence to our bedroom window.
They do come from a country where they talk loud as a matter of course, so at 2am we are treated to loud conversations through the wall, peppered with hearing them using taps, boiling kettles and, wonderfully, hearing them pee! (According to the electrician who did work while the house was empty the gap between our walls is narrow so noise travels easily.) If they had not banged their door hard enough to make the windows of our house rattle and loudly enough to wake me I would not be awake to hear their toileting though.
They are very hospitable, but this means having loud relatives visiting, when they have even more people to bang doors and make loud conversation. More cigarette butts left outside, dumped out their car door too, they will be picked up and dumped in front of their door soon though.
Living with noise, especially unnecessary noise, can be soul destroying. It sounds like the slamming of the door at your flat is louder than for us so it must be unbearable, make sure your landlord doesn't try to ignore your problem, if they don't get in touch about it soon contact them again. Don't let them forget about it.