Today I got wrongfully terminated from my job at JC Penney's?

I worked at JC Penney's and today I saw called into the office to talked to 2 lost prevention ladies. I was never told that employee's couldn't return merchandise without receipt, and several current employee's agree that we were never told that. Anytime I would return those items I would tell the returning associate that I use my 20% discount card and it was on sale/clearance. I never keep receipt because I shop almost everyday and it's hard to keep track of all the receipts. But they can look up receipt if you use a credit card and I always use my Visa card. I make sure to ask them to look up my rceipt and they never want to because they're lazy, so they just give me a return voucher. Apprently the amount on the return voucher has been more than I payed for them originally, and I have let the returning associate know that, however I was unaware that I was suppose to let them call a supervisor to adjust the price. So I explain everything to my mananger today in the meeting and he said he had to let me go. I will try calling corporate on Monday when they open do you guys have any idea what I should do about it?