Begin with If your Mac battery won't charge - Apple Support. I realize some of that information will be inapplicable, redundant, or premature, and that you already know the battery has discharged to to the point your Mac won't turn on. Read it anyway because it addresses some preliminary steps. For example, reset the System Management Controller (SMC) even though it's unlikely to fix anything immediately.
In addition to that please review Find the right power adapter and cable for your Mac notebook - Apple Support. Emphasis on the cable because it's frequently overlooked. It is entirely possible for that cable to charge other Macs, but not that particular MBP.
Then, continue with If your Mac doesn't turn on.
Only after exhausting all those steps, conclude with "If you still need help, please contact Apple Support."