If the plan charges the same amount for fewer months, your cost per month would increase.
This is because the total cost ($20) remains the same, but the number of months decreases. When you divide the total cost by a smaller number of months, the result is a higher cost per month. For example, if the service were to charge $20 for 2 months instead of 3, the monthly cost would be $20/2 = $10 per month, which is higher than the original $20/3 = approximately $6.67 per month.