Why are my texts being sent from my mom's phone number?

[AC Question]

Okay. So a few days ago my phone started doing this weird thing where the texts I send are being sent from my mom's phone number. I am pretty sure that is only MMS messages because I've been told that it happens when I send people photos and when I am in a group chat (which uses MMS) and i send a text another group chat pops up but with my mom and it appears she is saying what i had sent. Here are some additional details. I have a Samsung Galaxy S7 with Sprint, my plan is a business plan and my mom is also on that plan. When I got this S7 I used my Mom's upgrade to get the S7 for a cheaper price and I think that is why this is occuring, but I've had this phone for 2-3 weeks and this has only been going on for 2-3 days. Sorry if I'm blabbering I just want to provide all the information since the only problems similar to mine I could find on the internet were problems with iMessage.