After altering limits.conf, have you tried logging off and logging back into your account? I believe the changes won't come into effect unless you do this.

I feel u bro, same thing happened to me, but even worse I was on Windows using VS code, spent half an hour trying to find what's the problem :( then after a long search edited my compilation flags as shown here

Just typing ulimit -s into terminal should give you the default stack size. For me, it's 8192, i.e. 8 MiB.

To change the stack size in the code, you can use getrlimit() and setrlimit() system calls:

#include <sys/resource.h>

int main() {
    rlimit rlim;
    if (getrlimit(RLIMIT_STACK, &rlim)) return 1;
    rlim.rlim_cur = rlim.rlim_max;
    // You can set the fixed value instead of max value, e.g. rlim.rlim_cur = 1024 * 1024 * 1024
    // will set your stack size to 1 GiB
    if (setrlimit(RLIMIT_STACK, &rlim)) return 2;

    // Your code here...

    return 0;
}

Note that this example will work only for UNIX-like systems, so it's better to disable this code (using #ifdef, for example) when submitting to an online judge.

I failed D2 because of the exact same issue :(

Maybe you can just add ulimit -s new_value to your .bashrc file?