This question concerns Dutch law. Specifically, the Wet op het hoger onderwijs en wetenschappelijk onderzoek ("WHW") is applicable, as well as further rules seth forth by the Board of your university.
Pursuant to Article 7.10(2) WHW, a degree is completed once all study elements (individual exams) of the degree program are graded/completed, insofar the examencommissie (Examination Board) has not called for an additional investigation into the knowledge, understanding and skills of the candidate. Once a degree is completed, the University Board must grant the candidate the applicable degree pursuant to Article 7.10a WHW (e.g. by declaring that you are now a Master of Science).
Pursuant to Article 7.11(2) WHW, the examencommissie (Examination Board) must grant a diploma after completion of all study elements of the degree and after the University Board has declared that all procedural requirements for grant have been met. From Dutch parliamentiary history (Kamerstukken II 2008/09, 31 821, nr. 3, p. 57-58 (MvT)) (which is an authorative legal source for explaining provisions in Dutch legislation), it is clear that with "procedural requirements", the lawmaker referred to obligations such as the payment of tuition fees. The University Board is allowed to make such procedural rules.
Therefore, the University Board must grant you a degree if you have completed all ECTS, however the Examination Board may not grant the diploma if it deems that procedural requirments (different per university) were not met. It would thus be advisable to find out (via the university website) what these procedural requirements are.
If you request the University Board in writing (ex Article 4:1 and further Algemene wet bestuursrecht ("Awb")) to grant you the degree pursuant to Article 7.10a WHW and to make the declaration pursuant to Article 7.11(2) WHW, the University Board is obliged to make a written formal decision on your request, generally within 8 weeks at the most (ex 4:13(2) Awb). You have the right to appeal this decision before an administrative body.
Please note that amicable setlement with the university is in any case preferable. If that doesn't work however, I would advise you to contact a Dutch lawyer.