A little bit of electronics knowledge can be a dangerous thing!
Firstly, what voltage does the 'xiomi' power bank produce? The current rating is almost irrelevant, it's the voltage that matters. 'xiomi' is a brand name not a recognized specification.
The 1N4148 is rated to carry 0.2A before burning out so that wasn't a good choice of diode!
LM317 is also under current rated but with a suitably large resevoir capacitor could probably handle the average current needed by the SIM900A but it needs at least 1.5V more at it's input pin than it's output pin. So what voltage did you feed in to it and what value resistors did you use to set the output voltage and what value reservoir capacitor did you use?
Brian.