Strange intersection \cap symbol

Question

Whenever I use \cap in my tex, I get:

(which I don't like) instead of:

Any way to produce the second intersection symbol? The same happens with \cup.

Edit: this is what I always use:

\documentclass[a4paper,14pt,spanish]{article}
\usepackage{extsizes}
\usepackage[utf8]{inputenc}
\usepackage[spanish]{babel}
\usepackage[T1]{fontenc}
\usepackage{amsmath,amsthm,amsfonts,amssymb,amsbsy}
\usepackage{graphicx,color}
\usepackage{pifont,ulem}
\usepackage{multicol,enumerate,prettyref}
\usepackage{enumitem}
\usepackage{hyperref}
\usepackage{listings}
\usepackage{geometry}
\usepackage{mathrsfs}  
\usepackage{thmtools}
\usepackage{tikz}
\DeclareMathOperator{\nullspace}{null}
\DeclareMathOperator{\range}{rango}
\DeclareMathOperator{\re}{Re }
\DeclareMathOperator{\im}{Im }
\geometry{verbose,a4paper,tmargin=1.5cm,bmargin=2.2cm,lmargin=2.1cm,rmargin=1.9cm,headheight=0cm,headsep=0cm}
\setlength\parindent{0pt}
\theoremstyle{definition}
\newtheorem{teo}{Teorema}
\newtheorem{coro}{Corolario}
\newtheorem{defi}{Definici\'on}
\newtheorem{lema}{Lema}
\newtheorem{prop}{Proposici\'on}
\newtheorem{nota}{Nota}
\newtheorem{obs}{Observación}

\newrefformat{fig}{la figura \ref{#1}}
\newrefformat{teo}{el teorema  \ref{#1}}
\newrefformat{lema}{el lema  \ref{#1}}
\newrefformat{prop}{la proposici\'on  \ref{#1}}
\newrefformat{coro}{el corolario  \ref{#1}}
\newrefformat{sec}{la secci\'on \ref{#1}}
\newrefformat{cap}{el cap\'{i}tulo \ref{#1}}
\newrefformat{def}{la definici\'on  \ref{#1}}
\usepackage{mathabx}
\usepackage{blindtext}
\usepackage{multicol}
% comando recta
\usepackage{fancyhdr}
\usepackage{lipsum}

Answer 1

Please always consider providing a MWE. While doing this you can very often identify the cause for your problem.

Here I did this for you. I set up a document with your default preamble, added a body (\begin{document} \[ a\cap b\] \end{document}) and compiled. The problem is reproduced, so it is a working example. It remains to make it minimal. Therefore delete one package after the other, see if the problem is still there. Like this you get the following MWE:

\documentclass{article}
\usepackage{mathabx}

\begin{document}
\[a\cap b\]
\end{document}

Obviously the mathabx package is responsible for the redefined symbol.

How can one resolve the problem? We'll store the original definition of \cap in \oldcap, load mathabx, and restore the old \cap. You will have to do the same for \cup.

\documentclass{article}
\let\oldcap\cap
\usepackage{mathabx}
\let\cap\oldcap

\begin{document}
\[a\cap b\bigcup\]
\end{document}