I got a congratutory message on chrome that my MTN line have won #510,000

Hi Goodluck, that may be a fraudulent promo. If MTN is doing any promo, it will be advertised on their website: http://www.mtnonline.com and also in the media.
Also, MTN will never ask you to purchase recharge card and send to them or send money to them before they give you the promo you won.

ignore such message.