Bonitas don't pay up

I went on pensioen without a monthly income I had to discontinue my membership with Bonitasend of May 2022. With the poor post office service I received the statement from them that I owe them an amount. As it was to different invoices. I paid the highest amount. It was September 2022. In February an debt agency called me, and stated that I owe Bonitas money and was handed over to them. I checked for my statements and it showed actually Bonitas was owing me money. I contacted them and ask them to cancel the habnd over and pay the money they owe me. They asked for my banking info. I didn't received anything and contacted them again. Again they asked for my account details. I sent it again. Then I got an email, that they already sent me a authorized number to see the specialist and I am liable to pay the excess amount. I rep**** that they owe me the money and didn't receive any reply back. I think that they are not trustworthy.