Check the earths on the cylinder head are intact first, otherwise your clocks are probably shot. ( I have spare set you can have for cost of P&P)
No heating means that previous owner has probably bypassed the matrix or the bypass valve has seized. Change the valve for another one before you attempt to change the matrix. whatever you do, do not decide to remove the valve without replacing (unless you replace it with a genuine MK3 matrix) as these were a VW recall solution to ensure that the weak heater matrixes don't burst hot water over your feet (this hurts I know!)