Handed over for collection - Incorrectly billed as 36 months contract ended before hand over

They handed me over to lawyers for collection of monies. Since then i have investigated this account with the lawyers and noticed that both my contracts ended long before the handover and they have just been overcharging me for 4 years. The blue ray samsung hometheatre contact ended in 01/11/2016 and the note ended in 01/11/2018 yet i was charged till 02/02/2020. I have been trying to contact them its been 4 days no respond on email or the lawyers. I will not pay as Teljoy incorrectly billed me as the contracts for rent to own ended after 36 months and both was paid up at those dates as above. please refund me what i overpaid as well as close this account and clear my name off itc as this is Teljoys fault as per discussion with service agent contracts ended must be done automatically (as per riley discussed 31/07/2020)