Cannot send messages on phone (non-iPhone) with same mobile number as iPhone

Hello,

(I came here because iPhone tends to cause issues with SIMs.)

I have a second phone (Nokia 6300 4g) that I wish to use for my day-to-day usages, I would not like to change phone number if possible. However, I am totally unable to send messages. I can give and receive calls, but am unable to send or receive messages. I have turned off iMessage, but that does not work either. I can't find a solution online.