“The problem is my partner and I don’t know whether he is still on the mortgage as there has been a family dispute and know there is no communication between the them “
Your partner will be on the mortgage as any changes has to be notarised. Does your partner recalls going to a notary to take his name out of the title deeds & the mortgage ?
In the mean time some one is paying the mortgage instalments or has paid the mortgage off ??? If your partner is not paying his share than your family member is paying otherwise the lenders would have been chasing your partner.
If you cannot find out who took over Caja Banko. I than sugguest you get in touch with a gestor, who can find this information at a small fee.
Also do not overlook that your partner may have some equity in the property. Besides if your partner buys another property. He/She will have more than one property in Spain this will require more paper work, i.e. taxes & appoitment of a fiscal representative etc.