<human>: Can you condense the text into three sentences or less?

Hi folks, especially those with an understanding of UK rental law - 

25 months into our tenancy the estate agents who manage our private property have let us know that the owners of the property had been in touch about overdue bills. We had no idea what 'bills' they were referring to, as all the utilities and council tax we're already covering. We tell them so - they respond to say that we are liable to pay gas bills on our house, citing the part of our contract that covers this.

Up until this point we knew that the gas was centrally managed for the council estate our privately rented property is on. There are no gas metres, thermostats or any way of measuring/controlling our gas use, and we never received any bills (at least not addressed to us - we returned any mail addressed to someone else unopened).

Turns out the council issues yearly management/utilities bills for each property on this estate, so we received bills to the tune of £2.9k from the first month we moved in until March next year. (We'll receive another bill afterwards for the remaining months).

Now - the estate agents have spoken with the landlord [apparently] who has agreed to our paying installments of £500pm for the next 6 months. However, we're a bit put out that this never came to light either before we moved in or soon after, and are wondering if there's any way to contest the bill? 

It's a bit of a stretch, I realise, but we're not made of money and 'every little helps'.

If anyone out there has an understanding of UK property law and knows of any help we can get on this, please let us know!
<bot>: Estate agents have hit us with a £2.9k gas bill 25 months into our 3-year tenancy, which we are contractually obliged to pay. Is there any way to contest it due to its lateness?