Unable to cancel my Toekomsvonk monthly debit order

NOTE: There is no option under "Choose an Industry" for a "Non-Profit Company", so I selected "Home Services" instead. Please accept my apology...

I tried to cancel my membership and stop my debit order with Toekomsvonk NPC. I have send e-mails to both their "Lidmaatskap" and "Info" email addresses during July, but have not received any reply to date. I have also called their office number ***). A female took my call, but she was driving at the time, and promised to call me back on the same day. I never received a call-back from Toekomsvonk. I continued calling their number several times without anyone answering. I left voice messages asking them to call me back. Non of my calls were returned to date. I am frustrated as I am unable to stop the debit order without their cooperation.