Unable to send textmessage - imessage is only option

I have disable imessage on my Iphone 5s. I have also unregistered iMessage with my telephone number at Apple. But when I enter a mobiletelephone (to my mom, how has an iPhone) i only get the option to write an iMessage! But I dont have iMessage!! I have tried to delete alle messages from this phonenumber, and the contact info, and it still only gives the option to write iMessage - how is this possible! I have altså upgraded to last version of ios, and restated the phone.