  The nuclear matrix elements $M^{0\nu}$ of the neutrinoless double beta decay
($0\nu\beta\beta$) are evaluated for $^{76}$Ge,$^{100}$Mo, $^{130}$Te, and
$^{136}$Xe within the Renormalized Quasiparticle Random Phase Approximation
(RQRPA) and the simple QRPA. Three sets of single particle level schemes are
used, ranging in size from 9 to 23 orbits. When the strength of the
particle-particle interaction is adjusted so that the $2\nu\beta\beta$ decay
rate is correctly reproduced, the resulting $M^{0\nu}$ values become
essentially independent on the size of the basis, and on the form of different
realistic nucleon-nucleon potentials. Thus, one of the main reasons for
variability of the calculated $M^{0\nu}$ within these methods is eliminated.
