Hi Sparkleberry
Thank you for the kind reply.
However this is an old method for previous iphone versions
and it doesn't work proberly because the messages re-appear in a while...
I have repeated this method several times as suggested, but again...
all messages re-appeared.
I was asking if there is any improvement for that issue on iPhone 6 and IOS 8 +
I have read somewhere that mass messages may be deleted if you sign in online to your profile
..but I did't understand which profile and which website..
If anyone here knows anything about it, please let me know.