Samsung Galaxy Ace GT-S5830 can't receive incoming calls

After updating to version 2.3.7 of Android the device can't receive calls. Although it can call. The caller to my device is said to line was busy always, it happens from any kind of callers. Need to note, that incoming calls are saved to log, but without any notifications. I played with Profiles, WIFI settings, but it didn't help. baseband version: S5830XWKS2