The towel that felt like silk when you touched it in the shop just pushes the water around your skin after the first shower at home. You think you bought the wrong product. Most likely you did not.
To make towels look good on the shelf and feel soft in the hand, silicone-based softening finishes are applied at the last stage of production. This finish coats the surface of the fibre with a thin layer. It improves the feel, but it repels water. In other words, what wins the moment of sale loses the moment of use.
The solution is simple and takes patience. For the first two or three washes, wash the towel with little detergent and no fabric softener at all. Adding half a glass (about 100 ml) of white vinegar to one wash helps dissolve the remaining finish. After a few washes the towel's real character comes through. A good towel dries better over time. A poor towel shows what it really is once the finish has gone.