Today I did a lot of fixing in my code, but its way too buggy and I still didn’t fix all of them in 10 hours. Here are some bugs that is fixed and some changes:

1. Dynamic memory on Arduino Nano is running out, so I tried to use the U8G2 library for my mini screen instead of the Adafruit library, but its actually using more memory and is more buggy than Adafruit. In the end I discovered that it is my string commands that I am sending to my cellular module that is gobbling up all my memory, so I used F() macro to put them into flash memory.
2. My screen can’t connect after that change. I found out that by rendering a frame the screen library takes up 1024 bytes of dynamic memory, which is over the limit for my Arduino Nano.
3. Arduino UART is recieving corrupted data from my cellular module. After a bit, I figured out that the built in timer of the Arduino Nano is not precise enough for 112500 baud rate, so I lowered it to 9600.