Re-imbursemnet of the rental deposit

Just Letting have not paid back our deposit including accrued interest. It is now 53 days since we moved out of the property. They did not contact us until after 30 days we contacted them they told us they were busy since it was during the end of the month they promised to call us back which they never did. 45 days later I went back to their offices promised to contact me which they did after 5 days. They told us we had outstanding bills. We had sent proof of payments on 2 April 2015, we also resent it. They do not accept those payments. We moved in 0n 1 April 2013 moved out on 27 March 2015.