I'm not that good in coding.
Connect the bluetooth device ONLY, to a set of hardware serial pins, other than 0 and 1. Write a sketch that does nothing more than read data from the bluetooth device, using SerialN.available() and SerialN.read() (where N is the number of the RX and TX pins you are using.
It doesn't help to debug hardware in an already complex sketch. Test the hardware in a simple sketch. When you KNOW that the hardware works, you can incorporate the code to deal with it in the more complex sketch. Then, if the hardware doesn't work, there is a pin compatibility or resource issue that we might be able to deal with, or we might not.