Write a program that calculates the bill for a cellular telephone company. The company offers two types of service: regular and premium. Its rates vary depending on the type of service. The rates are computed as follows:·         Regular Service: R100 + The first 50 mins are free + R2 per minute for mins over 50.·         Premium Service:  R250 +a.       For calls from 6:00 a.m. to 6:00 p.m., the first 75 minutes are free; charges for more than 75 minutes are R1 per minute.b.      For calls from 6:00 p.m. to 6:00 a.m., the first 100 minutes are free; charges for more than 100 minutes are R0.5 per minute.Your program should prompt the user to enter an account number, a service code, and the number of minutes the service was used. A service code of r or R means regular service; a service code of p or P means premium service. Treat any other character as an error.For the premium service, the customer may use the service during the day and the night. Therefore, to calculate the bill, you must ask the user to input the number of minutes the service was used during the day and the number of minutes the service was used during the night.  Your program should then generate an invoice by writing the account number, type of service, number of minutes the telephone service was used, and the amount due to a file called bill.txt.

Sure, here is a Python program that fulfills the requirements:

def calculate_bill():
    account_number = input("Enter account number: ")
    service_code = input("Enter service code (r or p): ")
    day_minutes = 0
    night_minutes = 0

    if service_code.lower() == 'r':
        total_minutes = int(input("Enter total minutes: "))
        if total_minutes > 50:
            bill = 100 + (total_minutes - 50) * 2
        else:
            bill = 100
        service_type = 'Regular'
    elif service_code.lower() == 'p':
        day_minutes = int(input("Enter day minutes: "))
        night_minutes = int(input("Enter night minutes: "))
        total_minutes = day_minutes + night_minutes
        if day_minutes > 75:
            day_bill = (day_minutes - 75) * 1
        else:
            day_bill = 0
        if night_minutes > 100:
            night_bill = (night_minutes - 100) * 0.5
        else:
            night_bill = 0
        bill = 250 + day_bill + night_bill
        service_type = 'Premium'
    else:
        print("Invalid service code.")
        return

    with open('bill.txt', 'w') as f:
        f.write(f"Account number: {account_number}\n")
        f.write(f"Type of service: {service_type}\n")
        f.write(f"Number of minutes the telephone service was used: {total_minutes}\n")
        f.write(f"Amount due: R{bill}\n")

    print("Invoice generated in bill.txt file.")

calculate_bill()

This program first asks for the account number and service code. If the service code is 'r' or 'R', it asks for the total minutes and calculates the bill for regular service. If the service code is 'p' or 'P', it asks for the day and night minutes separately and calculates the bill for premium service. If the service code is neither 'r' nor 'p', it prints an error message. Finally, it writes the account number, type of service, total minutes, and bill amount to a file named 'bill.txt'.