First of all: never trust a single word estate agents tell you!
When does your contract end? What is the notice period? Is there a break clause?
Break clause means that you cannot terminate the tenancy before a certain period. Eg you could have a 1-year contract with a 6-month break clause and a 2-month notice; this would mean that normally your contract ends after one year, but you can end it before if you give 2 months of notice, however you cannot end it before 6 months. In this example, if you leave after 4 months, you would be liable to pay 2 more months of rent, ie till month 6, not till month 12.
Also, "liable" means you'd owe the landlord (not the estate agent) that money, but the landlord would have to come after you.
You should ask the Citizen Advice Bureau or a charity like Shelter.
Online you could ask on this forum https://forums.moneysavingexpert.com/ca ... ng-selling
but stuff said by stranger online is, well, to be taken with a truckload of salt.