How can I get my phone back!?!?!?

Okay so we have unlimited texting and not unlimited calling so I forgot it was then week day and i called my friend when i wasnt supposed to! So my mom took my phone away and its been gone for weeks! She told me i can get it back maybe if i have been cleaning and i have! I also promised to get good grades next year. I want to have it back but i dont no how to convince her!!! I sent her emails about if i can get it back and she never responds and always deletes them! Help!!!!!!!!!!!