output does not contain 'et al.', although the citation abbreviates to one author

Question

i have found many helpful answers to other question here, so i hope you can solve my problems as well. I'm currently writing my masters thesis and had to change to using biblatex, which brought a lot of problems along.

For me it looked like the solutions in biblatex – et al. beginning from second citation? would shorten several authors down to et al. after the second name, but it doesn't. I do always only get the first author and the year without the "et al."

I could only find other questions around here on changing the et al. into different languages or symbols, but not on creating it!

Here is my code:

\documentclass[12pt,a4paper,oneside]{article}
\usepackage[english, ngerman]{babel}
\usepackage[ansinew]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{hyperref}

\usepackage[backend=biber,
style=authoryear-comp, 
bibstyle= authoryear,
citetracker=true,
maxnames=99,
maxcitenames=2,
sorting=nyt,
uniquelist=false,
natbib=true,
useprefix=true
]{biblatex}

\usepackage[babel]{csquotes}
\addbibresource{literatur.bib}

\AtEveryCitekey{\ifciteseen{}{\defcounter{maxnames}{99}\clearfield{namehash}}}%
\DeclareNameAlias{sortname}{last-first}%
%
\let\oldmultinamedelim\multinamedelim %altes Trennzeichen speichern
\let\oldfinalnamedelim\finalnamedelim %altes Trennzeichen speichern
\renewcommand*{\multinamedelim}{~,\space} %
\renewcommand*{\finalnamedelim}{~\&\space} %

\AtBeginBibliography{%
\renewcommand*{\multinamedelim}{\oldmultinamedelim}%
\renewcommand*{\finalnamedelim}{\oldfinalnamedelim}%
}



\begin{document}\selectlanguage{english}

The study of \textcite[][]{Behr} \\
They say \textcite[][]{Behr} \\
..substantial lack of understanding" \parencite[][]{Behr}


\printbibliography[title={References}]
\addcontentsline{toc}{section}{References}\label{sec:ref}

\end{document}

with the article for literatur.bib:

@article{Behr,
 author ={Behr, M. and Wachsmuth, I. and Post, T. and Lesh, R.},
title ={Order and {E}quivalence of {R}ational {N}umbers: {A} {C}linical {T}eaching {E}xperiment},
 journal ={Journal for {R}esearch in {M}athematics {E}ducation},
volume ={15},
 year ={1984},
 pages ={323--341}
}

What comes out is: And as i just noticed there is another mistake: Why does it put spaces bevor the commas, isn't the ~ ment to prevent this? -> This was solved by deleting the ~.

Thank you for helping in advance.