Examine O.XII of CPC and you'll find your answer. Your post is vague as to how exactly the Claimant has 'relied' upon the document. The exact mode of reliance is the heart of the matter.
Examine applicability of CPC to arbitration proceedings and pull out judgments on this point. Pull out judgments on the point of procedure is handmaid of justice and not its mistress.
As a last resort if nothing works you can file a notice to admit documents and in case the tribunal is inclined to reject it (which it appears likely in your facts and circumstances), you can request the tribunal to rule on this application as part of the final award. Since only your final award is appealable under the Act and not these interlocutory orders and directions.
Examine applicability of CPC to arbitration proceedings and pull out judgments on this point. Pull out judgments on the point of procedure is handmaid of justice and not its mistress.
As a last resort if nothing works you can file a notice to admit documents and in case the tribunal is inclined to reject it (which it appears likely in your facts and circumstances), you can request the tribunal to rule on this application as part of the final award. Since only your final award is appealable under the Act and not these interlocutory orders and directions.