What to do if new company won't reply back after signed LOA?

Hi guys. I just want to get ideas to lift my spirits up.
I have been looking for a new employer for the past year and last month, a chance came up.

I was so happy and it was even an MNC company.
After I signed the letter of agreement, I followed up a week after and asked if my spass application has been submitted already.
HR said not yet since they need to post the job for the 28 days.
Okay, I understand, I think the HR didn't know that it was a requirement before.
Now, I tried to follow up after 1 month and 2 weeks, the HR won't reply to my messages or when I call, she will say she's busy.

I'm thinking they already found a replacement and just won't tell me.
It has been a tough year for me since it's s so hard to look for jobs that wants spass applicants and I think this is my only hope.

Any ideas what to do next?
Is the signed agreement really in effect that I am on board the company already?

But they still haven't applied my spass application because I always check the online status and nothing changes, the details shown are still my current spass.

Thanks guys.