i have oill in water vuxhall astra 1.7 td?

i have oill in the water the garage has cleand the water system out and checked the oill heat excanger out by presher testing and reset it up and run it sevrel times but no more oill in water . the oill that was ther
had copper in it can aney one help
i have a 1.7 astra td with air con