The problem is because you have iMessage activated on your iPhone so even though you switch to a non-iPhone, Apple still thinks that your number is using iMessage. So, anyone trying to send you a message from any apple device would be sending the message through iMessage. Unless the sender switches off iMessage and forces the message to be sent as an SMS, you’ll never get the message.
Turn Off iMessage on the iPhone, If you have the iPhone you can fix the issue easily.
The problem is with the iPhone still having its iMessage switch ON. This associates your number and your Apple ID to iMessage.
If you don’t have your iPhone, you can deregister your iMessage, you should be able to do that here. You need to enter your phone number and then a six-digit confirmation code, which is sent to your number.