Is this happening from any iPhone user who's sending you a text or everyone you know using an iphone sending you a text @Teej
As a process of elimination can you try your sim card in another phone and then ask an iphone user to send you a text.
I updated my Note 9 to Samsung One Ui / Pie a couple of weeks ago.
My partner and two adult children use iPhones and I've had no issues receiving text messages.
Like you I've used iPhones in the past up to the iPhone 6 Plus. I also made sure I deregistered my number from iMessage back then too.
It could be a network issue or the sender of the texts phone issue too. Can they receive texts from you Ok ?
Current Phone ~
Samsung Note 20 Ultra 5G SM-N9860_256Gb SnapDragon 865+
Samsung One Ui 3.1/ Android 11.
Not all iPhone users as my friend can text me using hers. Also issues with Samsung on o2 not receiving texts from them. Everyone is getting mine, just not the other way. Been to shop, they are baffled been and had a sim change, still nothing. Come on Samsung there must be a fix.
My daughter has the iPhone X and their latest update broke the notification and messaging service which could be the cause of some iPhones working and others not. Hope this helps.
Getting an image placeholder from iOS phones when receiving texts, but they don't download
and are removed from group chats and become direct from a contact.
Note 10+ 5G SM-N976U
One UI 2.0
Android security patch level Feb 1, 2020