That's a shame Fanjeera. It is more likely to be your technique than the detergent you used. With a lace piece, you have to be very gentle with the hair when the knots are wet, because the lubrication of the water makes the knots liable to come undone. Even more so if you are using soap and/or conditioner.
When you wash your piece, try to keep the soap and (especially) the conditioner off the base and the knots. Crumple the base in your hand, and use it to hold the hairpiece, so that it is like you are washing a ponytail of hair, rather than a flat surface. Put the soap and/or conditioner on the 'ponytail' about an inch away from the base, and work it down the length of the hair. Rinse the same way, so that the water is running down the hair away from the base. Then, when the cleaning/conditioning process is finished, give the whole piece, including the base, a final rinse in clean water.
Also, don't scrub the hair on the base, just squeeze soap etc. through the 'ponytail'. You can comb the hair with the conditioner in it to get rid of any tangles, but don't pull it from the base - grip the 'ponytail' tightly with your fingers an inch from the base, so that the pull is against your fingers, and not against the base.
Knot sealer can help prevent this problem, but you may find if you are careful that you don't need it.
Does that description make sense?
noah
. i also put the shampoo right there