While I am sure that piwik is an excellent solution for many applications
it is too powerful for my simple website.
So sometime ago I decided to delete it.
That is when my problems began.
For some reason the files do not belong to the user
on my web server but to another (root i suspect).
After much experimentation with my limited knowlege of php and posts on this forum
most of it got deleted.
However there is still a folder on my public_html calles piwik,
which i am unable to delete despite an exchange with the authors of the package.
Of course my web host provider could delete it with with
superuser privileges but they have better things to do.
After some years it really is an irritation.
I thank you for your suggestion to remove the @ in front of rmdir.
I am at an internet cafe and do not wish to log into my web server at the moment
(fear of a keylogger)
but when i am at my computer i will try this
only i think that i tried this at my last attempt a year ago
and things remained the same.
I will keep trying. You never know and like /piwik I am very persistent.