Shares of

CSG Systems

(CSGS) - Get Report

skyrocketed 49.4% Wednesday, a day after the company said its biggest customer,

AT&T

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(T) - Get Report

, agreed to dismiss a demand for arbitration with the company.

The company's shares were recently up $13.94 to $42.

Last month, AT&T sought arbitration, claiming that CSG violated the terms of the agreement between the companies, causing shares of CSG to plummet. AT&T alleged that CSG failed to fulfill its obligations for telephone software and services.

Yesterday, the companies agreed to amend their contract in a way they believe is "mutually beneficial."