I Can't find DTMF Decoder HT9170B IC in Proteus
While I expect you could code up a model of the thing, I have to ask why anyone would bother simulating something like that?

In my experience simulations shine for little bits of analogue (Filters, control loops, thing like that where you want a quick bode plot to sanity check your calcs), and for complex digital where modelsim and friends rock (Also for some RF and SI issues if you have those tools), but I don't think it would have ever occurred to me to bother simulating something like a DTMF decoder that I was buying in as a chip. 

We sometimes get students here convinced that simulating an entire board design is the common thing to do, it nearly never is and is something very seldom done outside a certain sort of academia.