Share trading in MTN, Africa's biggest mobile operator, has restarted after earlier being suspended following a huge fine imposed by Nigerian authorities.
Trading in MTN Group was halted in Johannesburg after the stock fell 8%.
Dealings later started again after the company said it was in talks with Nigerian authorities about reducing the record $5.2bn (£2.7bn) fine.
The sum amounts to double MTN's annual profits last year.
The Nigerian Communications Commission imposed the penalty for failing to cut off unregistered mobile users, giving MTN just two weeks to pay.
The company said on Monday it was in talks with the Nigerian presidency, internal security agency and the communications regulator about the fine.
Chief executive Sifiso Dabengwa, who used to run the company's Nigerian operations, is understood to have flown to Abuja in a bid to negotiate a lower penalty.
Nigeria is MTN's biggest market, with 28.5 million subscribers, followed by Iran and South Africa.
The company's shares had fallen by about 25% since the fine was announced on Monday last week, wiping about 60bn rand (£2.7bn) off its market value, with the company now worth about £13bn.
The stock was down 5.5% after trading recommenced.
Analysis: Matthew Davies, Africa Business Report editor, Johannesburg
There's more to this story than meets the eye. It's not simply a case of a company failing foul of regulatory authorities and getting a slap on the wrist - some analysts say this $5.2bn slap is enough to break or seriously bruise MTN's wrist.
The fine was imposed because MTN failed to cut off unregistered SIM cards, which was regarded as crucial to limiting the communications of Nigeria's various armed criminal and terrorist groups.
It is thought that the kidnapping of a former finance minister, Chief Olu Falae, was the thin end of the wedge for the Nigerian authorities.
He was taken by armed men at the end of the September. It transpired that the phone the kidnappers were using to communicate their ransom demands had an unregistered SIM card from MTN.
That is when the Nigerian government is thought to have finally run out of patience with the mobile operator.
Admired and valued
MTN has 231 million subscribers in 22 countries across Africa, Asia and the Middle East.
In September, the company was named as most admired brand in Africa in the Brand Africa 100 awards, beating Samsung, while it was also awarded the continent's most valuable brand - worth $4.6bn (£3bn).
MTN was South Africa's second mobile operator when it was set up in 1994 after the fall of apartheid.
It began its expansion across Africa four years later with operations in Rwanda, Uganda and Swaziland.