If a subscriber claims a reduction in charges as a result of difficulties or irregularities during the call, he may be requested by his Administration to supply copies of the message in question as transmitted and received. If the faults are clearly attributable to either of the subscribers, no reduction of the charge shall be made. If the difficulty was due to the telex service, the chargeable duration of the call shall be reduced to the total period during which telex conditions were satisfactory.