Here's a link to the Firmware: Johnny Paranoia's Other Blog: Huawei U8520 Duplex
There seems to be only 2 available.
I think it may be necessary to follow the Huawei Upgrade Procedure to get the phone back to "out of the box state".
Quote from User FAQ's U8800. (This seems to be standard procedure for Huawei Smartphones.
2.1 Forced Upgrade
The forced upgrade method is as follows:
Note: After the forced upgrade, all user data (contacts, text messages, and multimedia messages) will be lost.
1. Go to Support - Huawei Device Co., Ltd..
and search for the latest U8150 version, download it to the local drive, and uncompress it to extract the upgrade file.
2. In the SD card root directory, create a new folder named dload. Take the extracted upgrade file, UPDATE.APP, and copy it to the dload folder.
3. Insert the SD card into the mobile phone.
4. When the mobile phone is powered off, press the Volume +, Volume -, and Power keys at the same time to initiate the forced upgrade.
5. After the upgrade is complete, restart the phone, and continue to use as before.
Make sure your phone battery is fully charged before carrying out any Firmware Upgrades, and do not do anything with the phone until the procedure is finished otherwise you mat end up with a "BRICK"
The above info is usually in the Download Firmware. Neil.