Cannot delete photos from photo stream on iphone5 iOS 7.1

Hello,

I cannot delete a certain group of photos from my photostream on my iPhone5 with iOS 7.1.

These certain photos only appear on my iphone photo stream. They are not present in my iCloud on my macbook pro or my iPad.

They are not present in my iphoto albums.

I have deleted them from my camera roll 6 months ago but they still appear in my iPhone photostream

When I try to select any photo of this certain group the Trash icon, bottom left corner, remain grey and cannot be clicked to delete the photos. If I choose any other photo outside this certain group, there is no problem in deleting it.

I tried syncing with my macbook many time with no luck.

Can someone please help

Cheers