Can't help I'm afraid mate, but I can sympathise.
The heater matrix in my last golf didn't work the whole time I had it.... a year and a half! 2 winters.
It got so cold in there that the windscreen froze on the inside every morning.
It was harsh and gross, coz it used to get so condensated (and very occasionally I resorted to anti-freeze!)
Hope you get it sorted, I'm sure you will, surely there can't be anyone out there who would put up with it for as long as me???
x