New [SGS2][2.7.27] My phone is sending SMS messages on its own

I noticed this already on 2.7.20... but I wanted to make sure it wasn't me who turned on some weird function, so I did a full wipe yesterday (did a factory reset, formated external SD card, formated internal storage, formated data, cache, system... everything that was possible) and then installed the 2.7.27 version.
When the installation finished, I set up Xiaomi synchronization, entered access points for Internet and MMS, entered my Google account settings for the Play store to work and I installed the Facebook application. I was already a bit tired then, so I went to sleep and left the phone turned on the whole night. As I woke up today I checked my SMS usage and I noticed that I my phone sent 14 SMS messages overnight. WTF!? And all of them to "0106571203855xxx". (They are nowhere to be seen on my phone, in "Messages".)

I have two ideas what this number could be:
- when I enabled Xiaomi sync, an SMS had to be sent in order to enable it. The service has been successfully enabled, sync works perfectly... but maybe my phone is still trying to get some kind of response by retrying and sending SMSs???
- when I tried to enable Cloud messaging, an SMS had to be sent in order to enable it. I confirmed this action but nothing happened. Cloud messaging remains disabled... but maybe my phone is still trying to get some kind of response by retrying and sending SMSs???

The worst thing is that I don't have an unlimited billing plan so this could bug could easily make me a lot of costs.

I temporarily "solved" the problem by deleting out the SMS center number.

that was weird, do you happen to know who's the owner of that number? and where did you check your SMS usage?

I have no idea... it's not from my country, for sure: 1) none of the numbers in our country start with 010, 2) it's too long.

I checked my SMS usage by sending an SMS with a keyword to my operators short number, which is used to check billing plan status - it gives me information about minutage used, SMS usage, data usage, etc.

For me to investigate the problem, I entered back the SMS center number today from 10h to 17h... and my phone sent 10 SMS messages:
at 10:07, 10:10, 10:11, 10:36, 10:37, 10:53, 10:57, 14:12, 14:13, and 16:56 .

Now I disabled the Xiaomi sync and I'll see if the phone would stop sending SMS messages on its own...

Yep, it's Xiaomi sync!!
I turned it off (deleted account) and my phone stopped sending those countless SMS messages.

da fuq ?