Following news that Saudi operator Mobily requested a referral to arbitration after falling out with rival Zain over claims of an unpaid bill of SAR2.2 billion ($587 million), Zain has said it only owes SAR13 million.

Zain has said that although it does not think the companies’ agreement enables the dispute to be subject to arbitration, it has “notified Mobily of its selection of an arbitrator without prejudice to Zain’s concerns.”

“It is not clear to Zain the basis for Mobily’s arbitrary demands,” the operator said in a statement, adding that “Zain has used Mobily’s network pursuant to an agreement, and it has always thoroughly reviewed the demands sent by Mobily. Zain has settled the amounts it owes, except for a currently outstanding amount of SAR13 million.”

The statement also claims that some of Mobily’s demands contradict the regulatory resolutions issued by the Communications and Information Technology Commission, the country’s regulator.

The two signed an agreement in May 2008 to cooperate across a range of services including national roaming and site sharing.

Mobily claims it is owed SAR2.2 billion as of November 2013 and has been unsuccessfully trying to reach an amicable settlement, which is why it decided to revert back to arbitration.

In an interview with Reuters, Zain Saudi’s CEO Hassan Kabbani said that Mobily failed to provide documentation that would substantiate its claims, describing the amount of SAR2.2 billion as unreasonable.