RCurl - submit a form and load a page

问题:

I'm using the package RCurl to download some prices from a website in Brazil, but in order to load the data I must first choose a city from a form.

The website is: "http://www.muffatosupermercados.com.br/Home.aspx"

and I want the prices from CURITIBA, id=53.

I'm trying to use the solution provided in this post: "How do I use cookies with RCurl?"

And this is my code:

    library("RCurl")
    library("XML")

    #Set your browsing links 
    loginurl = "http://www.muffatosupermercados.com.br"
    dataurl  = "http://www.muffatosupermercados.com.br/CategoriaProduto.aspx?Page=1&c=2"

    #Set user account data and agent
    pars=list(
            id = "53"
    )
    agent="Mozilla/5.0" #or whatever 

    #Set RCurl pars
    curl = getCurlHandle()
    curlSetOpt(cookiejar="cookies.txt",  useragent = agent, followlocation =TRUE, curl=curl)
    #Also if you do not need to read the cookies. 
    #curlSetOpt(  cookiejar="", useragent = agent, followlocation = TRUE, curl=curl)

    #Post login form
    html=postForm(loginurl, .params = pars, curl=curl)

    #Go wherever you want
    html=getURL(dataurl, curl=curl)
    C1 <- htmlParse(html, asText=TRUE, encoding="UTF-8") 
    Preco <- C1 %>% html_nodes(xpath = "//li[@class='preco']") %>% html_text(xmlValue, trim = TRUE)

But when I run the code I only get the page behind the form, not the intended page:

"http://www.muffatosupermercados.com.br/CategoriaProduto.aspx?Page=1&c=2"

I have also tried to play with cookies, but with no luck.

Does anyone have an idea on how to submit this form and load the correct page?

tks in advance...