Conveyancing Brisbane

The real estate agent that used to be the managing agent for the vendor is now our managing agent for the property. They remitted all the rent without any adjustment to the vendor prior to the settlement. They told us that the vendor’s solicitor should have made an adjustment at settlement. But they did not. Our conveyancing agent was not aware that there was any rental adjustment as the contract said "vacant possession". We had asked the realestate agent to change it, but it did not happen. How can we get our rental income from the vendor if he refuses? Whose responsibility is it to chase the vendor for the money? Did our managing agent do anything wrong?