can’t do MNP from GTN to rakuten mobile?

please help if you know where I’m going wrong because I can’t figure it out😭

I got the GTN mobile unlimited plan before I came to japan and now that I’ve lived here for a bit i want to terminate the contract and use rakuten mobile saikyo instead. but during my application for rakuten when I get to the phone number part, it won’t let me port it through mnp since GTN uses the rakuten service for my phone already.

Is there no other way to do this besides getting a whole new number?? i dont want to change all my stuff again😭🙏if you know or have a different unlimited recommendation to switch to please help me out here i really don’t like GTN

by Prestigious_Bus_6145