if else function c++ not returning valid values

hello i have a if/else statements in a function that is not returning valid values... the program ask the user for an account number the value is then passed to the GetCopayment function and then checks if the account number is over 100,000 but less then 399999 it should return 1, if the account number is <=400000 but less then 599999 it should return 2 but instead keeps returning 1 i don't know why... i have posted my code below

#include <iostream>
using namespace std;
double GetCopayment(double account_number);

int main(void)
{
	char patient_member_check;
cout<<"Is the Patiend a M)ember or N)on-member? ";
cin >> patient_member_check;

if((patient_member_check=='m')||(patient_member_check=='M'))
{
	int account_number;
	double charges;
	cout <<"Please enter your account number ";
	cin >> account_number;
	cout <<"Please enter additional charges";
	cin>> charges;
	GetCopayment(account_number);
	cout <<GetCopayment(account_number);
}

else if((patient_member_check=='n')||(patient_member_check=='N'))
{
	cout <<"your not a member";

}
}

double GetCopayment(double account_number)
{
	if((account_number >=100000)||(account_number <=399999))
	{
		return 1;
	}
    
	else if ((account_number >=400000)||(account_number <=599999))
	{
		return 2;
	}
}

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