Contacts and calendar items automatically eleted

Today Ive noticed that some of my contact' names where missing, but they phone numbers still were loaded.

Calendar items were all deleted.

Now checking my phone I see that all contacts are ok! Calender also.

Why did it happened? How can it be permanently fixed?

Ive an Iphone 4, IOs 5.0.1.

Thanks!!

Btw: thanks Apple for selling me a product and give me no phone nor straigth support.