i need to remove a number from my imessage/iCloud

ok so I've been using a straight talk phone pre paid number. but my cousin recently got a new phone, she added a line and then took her old phone and put it on the new line and gave me that phone. I set it up but my iMessages aren't working properly..when I went to settings on my iPhone it says my old number, and my APPLEID listed for iMessages. I figured I may have set something up wrong or tapped on the wrong thing. the prompts pop up fast and my eye sigh isn't so great so anyway.. I went to apples web site and added the new number to trusted numbers and also to the message section but it wouldn't let me delete the old number at all it only let me add the new one. so how do I fix this? I think It got set up wrong and im not sure how to get it so it works with the new number.. the old numbers pre paid plan runs out after today and as of right now all my messages are being sent only from my appleID because under message settings on my phone I has both phone numbers listed but the new number has the "thinking symbol" on it and it just keeps spinning. if I try to tap on it the phone prompts me with "this number will be removed from iMessage" so I hit cancel because thats not what I want.. I want to remove the other number not the new one. any ideas?