Why does my Android 2.2 powered Samsung Galaxy I5510 receive duplicated messages (SMS)? I own a brand new Samsung Galaxy I5510 (Android 2.2). Everything works fine and I really like the device.
My problem is:
Every time Some times I receive a message from a phone number that is not in my contact list, the phone continues receiving it every few hours.
Facts I pointed out:

The time between those messages is not constant.
It never happened when the number was in my contact list.
Deleting the thread does not solve the problem.
The senders do not fool me and send the message again and again.
It seems to stop after a day or two.
restart of the phone does not solve the problem.
I am not sure if it really receives the message again or if it just copies the old one.

Does anybody has an idea what could cause the described behavior?
Thank you!
EDIT: Another point why it is not likely to be a provider issue: I never received a duplicated message while the phone was turned off. Means: I never switched the phone on in the morning and received one or more such messages instantly.
EDIT 2: I looked through all the phone log. It happened by now for two numbers. Both were not in my contact list. The occurencies and their time of day are:
+491773**4537
15:38
17:23
19:19
21:41
00:37
phone off
13:20
16:12
20:48
phone off
09:59
10:16
14:10
phone off
12:46
21:04
--------
13 times

+491635**4554
23:39
phone off
12:20
13:09
14:44
16:16
17:51
19:28
21:02
23:39
phone off
07:28
08:16
09:32
10:51
12:17
15:28
17:00
18:27
20:04
21:21
22:47
--------
20 times

Message from numbers that did not repeat:
+491762**21169
+491797**1598
+436508**7821
+336782**105
The problem simply disappeared after a few weeks. I guess the carrier changed something or my phone got updated without informing me... Who knows.