Another alternative would be to call the supermarket and relate your experience and ask for a refund, tell them that you intend to keep the chicken as you are taking the issue further but can show it to them if they require. Freeze the chicken.
Call or write to the Health Minister and explain what has happened. Ask him how you can proceed with further investigations. It is in their interest to determine how poisoners chicken is being sold.
Write/email the chicken manufacturers/producers and relate your experience. Tell them you would like to know how this occurred and that you have frozen the chicken. Also, what assurances can they give that this will not occur again. Let them know that you were poisoned and whether they will compensate you.
If you get no where, contact the media.