@Bk2020 did you sign up under the Lunar promotion ? Don't switch, you will lose it. Instead, try to conserve data. Do such things as enable updates over WiFi, turn off all apps from using background data but the essentials ones. You could turn data off and enable it only when you need it and to send/recieve mms messages.
I'm wondering why you would buy 400mb of data for $20, when for $30 you can get 1gig. Also, which plan are you on? If you run out of data every month and have to spend $20, then you should look for a plan with more.
If you didn't sign up during the Lunar promotion , then consider switching up. Check to see if there are any bonuses that you may lose, depending upon when you signed up. If you are unsure, post the date and month joined, the applicable bonus and ask here. Also if you do decide to change your plan, set the change to start on your next cycle, do not change immediately, because you will lose both the remaining balance in your current cycle and be charged for The new one.