Different column number in rows

The following provides a much cleaner interface, if you're interested in spreading out the contents beyond column 1 evenly:

\documentclass{article}
\usepackage{booktabs,multirow,tabularx}% http://ctan.org/pkg/{booktabs,multirow,tabularx}
\newcommand{\makecell}[2][@{}c@{}]{\begin{tabular}{#1}#2\end{tabular}}
\usepackage[margin=1in]{geometry}% Just for this example
\setlength{\parindent}{0pt}% Just for this example
\begin{document}

\begin{tabularx}{\linewidth}{c X}
  \toprule
  xxxxxxx & 
    \hfill yyyyyyyyyyyyyy \hfill\null \\
  \midrule
  \makecell{aaaaaaa \\ $E = \lambda \cdot x$} & 
    \hfill bbbbbbbbbbbbbb \hfill\null \\
  \midrule
  \makecell{cccccccc \\ $P = \beta \cdot x$} & 
    \hfill \makecell{ddddddddddddddddddd \\ (4)} 
    \hfill \makecell{eeeeeeeeeeeeeeeee \\ (3)} 
    \hfill \makecell{fffffffffffffff \\ (1)} \hfill\null \\
  \makecell{gggggggggg \\ $I = \gamma \cdot x$} & 
    \hfill \makecell{gggggggg \\ (6)} 
    \hfill \makecell{ddddddddd \\ (5)} 
    \hfill \makecell{ggggggggg \\ (3)} 
    \hfill \makecell{dsdsdsds \\ (1)} \hfill\null \\
  \makecell{Calidad canal \\ $\Delta = \delta \cdot x$} & 
    \hfill \makecell{aaaaaaaaaaaa \\ (5)} 
    \hfill \makecell{hhhhhhhhhhhhhhhhhhhhhh \\ (3)} 
    \hfill \makecell{rrrrrrrrrrrrrrrr \\ (1)} \hfill\null \\
  \bottomrule
\end{tabularx}

\end{document}

The entire structure is set in a tabularx consisting of two columns. The second X-column removes the guesswork of trying to figure out how many columns to use and how wide the table should be. \hfills spread the content evenly within the column, while \makecell (similar in definition to that provided by the makecell package) stacks elements vertically.

The above code is clean and allows customization by changing the definition of \makecell (if needed).

To vertically center the H2 cell, you will need to also use the multirow package.

\documentclass[a4paper]{article}
\usepackage{multirow}
\begin{document}

\begin{tabular}{ c c c c c }
  H1 & \multicolumn{4}{c}{\multirow{2}{*}{H2}} \\
  T1 \\
  T1 & test & \multicolumn{2}{c}{text} & text \\
  T1 & \multicolumn{2}{c}{text} & \multicolumn{2}{c}{text} \\
  T1 & text & text & text & text \\
\end{tabular}

This code will produce:

To make the row with 3 text's have evenly sized tables, I assumed 13 cells would be required. However, the sizing was still unusual until I added a row of blank cells to the bottom.

\begin{tabular}{ c c c c c c c c c c c c c }
  H1 & \multicolumn{12}{c}{\multirow{2}{*}{H2}} \\
  T1 \\
  T1 & \multicolumn{4}{c}{text} & \multicolumn{4}{c}{text} & \multicolumn{4}{c}{text} \\
  T1 & \multicolumn{6}{c}{text} & \multicolumn{6}{c}{text} \\
  T1 & \multicolumn{3}{c}{text} & \multicolumn{3}{c}{text} & \multicolumn{3}{c}{text} & \multicolumn{3}{c}{text} \\
  & & & & & & & & & & & & \\
\end{tabular}

This produces:

There were a few wrong \multicolumn commands in your code.

Hope this is what you wanted

Code:

\documentclass{article}
\usepackage{multirow,booktabs}

\begin{document}
\begin{table}[!hbt]
   \centering
   \caption{caption} \label{tab:table}
   \begin{tabular}{c c c c c c c c c c c c c}
      \toprule
      xxxxxxx & \multicolumn{12}{c}{yyyyyyyyyyyyyy} \\
      \midrule
      aaaaaaa & \multicolumn{12}{c}{\multirow{2}{*}{bbbbbbbbbbbbbb}} \\
      $E=\lambda \cdot x$ & \multicolumn{12}{c}{} \\
      \midrule
      cccccccc & \multicolumn{4}{c}{ddddddddddddddddddd} & \multicolumn{4}{c}{eeeeeeeeeeeeeeeee} & \multicolumn{4}{c}{fffffffffffffff} \\
      $P=\beta \cdot x$ & \multicolumn{4}{c}{(4)} & \multicolumn{4}{c}{(3)} & \multicolumn{4}{c}{(1)}\\
      gggggggggg & \multicolumn{2}{c}{gggggggg} & \multicolumn{2}{c}{ddddddddd} & \multicolumn{4}{c}{ggggggggg} & \multicolumn{4}{c}{dsdsdsds}  \\
      $I=\gamma \cdot x$ & \multicolumn{2}{c}{(6)} & \multicolumn{2}{c}{(5)} & \multicolumn{4}{c}{(3)} & \multicolumn{4}{c}{(1)} \\
      Calidad canal & \multicolumn{4}{c}{aaaaaaaaaaaa} & \multicolumn{4}{c}{hhhhhhhhhhhhhhhhhhhhhh} & \multicolumn{4}{c}{rrrrrrrrrrrrrrrr} \\
      $\Delta = \delta \cdot x$ & \multicolumn{4}{c}{(5)} & \multicolumn{4}{c}{(3)} & \multicolumn{4}{c}{(1)} \\
      \bottomrule
   \end{tabular}
\end{table}
\end{document}