Is it true that soaps are salts of sulfonic acids though some have been made from alkyl sulphonates

It is false.

Soaps are sodium and potassium salts of fatty acids.

Synthetic detergents on the other hand, are salts of long-chain alkyl sulfuric  acids (sulfonic acid) or alkylbenzenesulfonic acids, rather than carboxylic acids.

Explanation:

Soaps are sodium and potassium salts of fatty acids. Soaps are made by the process of saponification in which an alkali is added to a fat or oil and then boiled to produce a salt of the fatty acid known as soap. The alkali used may be sodium or potassium hydroxide. However, the advantage of potassium soaps is that are more soluble and lather more easily.

Salts of sulfonic acids or alkylbenzenesulphonates are known as detergents. Unlike soaps, they are not salts of fatty acids and are more soluble in hard water, because the polar sulfonate ion of detergents does not readily bind to calcium and other ions found in hard water. Thus, detergents are more widely used as cleansing agents than soaps