Gas leak and reimbursement

Hi,
I have a dispute we have with our landlord’s agent. We moved in our current apartment (3 people) in January 2012 and from January until September we were paying on average around 70 EUR per month for gas and electricity. We recently received the end of year reconciliation and we were requested to pay and additional amount of 970 EUR, exclusively for gas for a 9 month period. This amount seemed exaggerated to us, especially since we didn’t need to use heating for at least 5 months (May-September), while the agent suggested that the amount was normal. We paid the invoice for this, but we also called a technician to take a look in case there was a gas leak. He found a leak in the basement and we were charged 286 EUR for the repair. We informed the agent and asked him to pay the whole amount for the technician’s work as well as at least a percentage of the 970 EUR for the reconciliation the energy provider, since this amount is extremely elevated largely due to the gas leak. But he refused to do so and suggested that it not his responsibility to cover those costs.

Could you please advise us on this?

Thanks a lot for your help