How to eliminate noise that has the same frequency of my signal
Whenever the desired signals and undesired signals are at the same 
frequency band, you can't use the bandpass filter because it will remove both the desired and undesired signals. 

In such cases statistical characterization for filter design is needed. Means you need to find out those statistical characteristics of background voice (noise) which differs your required signal from the noise. Examples include variance, expectation / mean or there can be others depending upon background noise, you might need to design adaptive filter if the noise characteristics changes with time.