Hi guys sorry for the late reply,
the problem is kind of sorted. I found another dealer who said that they will change the coolant for 35 euro.
So I ll probably book my car in some time next week and let them do the job.
Thank you for all the replies and advices was really helpfull.
Since I am already here I need to ask you have any of you had a problem with leaking rain water in the boot where the spare tyre is.
2 weeks ago I opened the boot and accidently saw a big pool of water where the spare tyre is.

My Mazda is a hatchback version and it s year 2004 if it helps.