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A man walks past a MTN notice board in Lagos, on October 27, 2015.  Nigeria's telecommunications regulator has fined South African mobile giant MTN $5.2 billion for missing a deadline to disconnect unregistered SIM cards, the company announced on Monday. The penalty saw shares in Africa's largest telecommunications company crash more than 12 percent to 167 rand on the Johannesburg Stock Exchange, the biggest fall the firm has suffered in a day since November 1998. AFP PHOTO/PIUS UTOMI EKPEI        (Photo credit should read PIUS UTOMI EKPEI/AFP/Getty Images)
A man walks past a MTN notice board in Lagos, on October 27, 2015.  Nigeria's telecommunications regulator has fined South African mobile giant MTN $5.2 billion for missing a deadline to disconnect unregistered SIM cards, the company announced on Monday. The penalty saw shares in Africa's largest telecommunications company crash more than 12 percent to 167 rand on the Johannesburg Stock Exchange, the biggest fall the firm has suffered in a day since November 1998. AFP PHOTO/PIUS UTOMI EKPEI        (Photo credit should read PIUS UTOMI EKPEI/AFP/Getty Images)

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    MTN chief executive quits after $5.2bn fine

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MTN chief executive quits after $5.2bn fine

Nigerian regulators imposed a penalty after the company failed to cut off customers who used unregistered SIM cards. CNN's Eleni Giokos explains.

MTN chief executive quits after $5.2bn fine

Nigerian regulators imposed a penalty after the company failed to cut off customers who used unregistered SIM cards. CNN's Eleni Giokos explains.