iMessage has been a common messaging platform for iOS users but if you have recently swap to a non-iOS device, do you know you might not see messages that are sent to you?
When you swap to a non-iOS device, the same phone number that you are using is still registered with iMessage. This will lead to people sending iMessages to you from their iPhone as its shown to them that you number is registered with iMessage.
Apple has created a a support page to allow you to deregister from the iMessage system. This is only applicable for users who have swapped from iOS to non iOS device.
If you are holding on to you old iPhone, you may put the sim card back in and turn iMessage off from the setting.