Group texts sent as iMessage

Hi,

I am regularly sending group messages to people to a bunch people I work with. All the recipients but one have an iPhone, the one that doesn't is on Android. The messages are being sent as iMessages regardless, and the Android recipient never receives them. Any way to fix this? The Android recipient used to have an iPhone (with the same phone number), so I suspect this is where the problem comes from, but I've no idea how to fix it.

Using iOS 9.2.1. The settings for messages are as follows:

• iMessage turned on
• Send Read receipts turned on
• Send as SMS turned on
• SMS/MMS
  • MMS messaging turned off
  • Show subject field turned off
  • Character count turned on

Thanks in advance,

Arnaud