Getting a full refund of all amounts paid to a developer due to a breach of contract

Dear sir/madam,

In January 2017, I purchased a property from a developer. The original booking was for a unit in (.......). After initial payments, I was informed that the unit was double-sold (under dispute) and the previous owner was not willing to sign a release NoC.

A swap unit was offered in (.......) - due to be delivered in a few months. Due to construction issues, even 2 years later was not ready for delivery. After escalation, a unit in (.......) was offered as a second swap. All payments were completed on time for each of the units.

Almost 3 years of following up passed now since making the final payments in April/May of 2019. I was not informed that the unit is under group mortgage and Title Deed can not be issued until the mortgage is cleared. Always promises that the unit is on priority for clearance.

What is the possibility of getting a full refund of all amounts paid under "breach of contract" or any other applicable grounds?

I would also like to know a cost estimate for any legal proceedings.