Family Dollar complaint: Blank check fraud robbery

I had bought a cell phone and phone time from there and was going to write a check but I just started using checks for the first time and one of the two employees told me to just sign it and leave it blank that they can fill it out for me later when they count their money at end of night I’m pretty sure both workers know each other and may be possibly stealing from the store or customers. Of course I did not leave them the check for she was planning to rob my bank account I believe by signing it to herself and mobile check cashing cause she checked to make sure it has that option to do so on back of check I tried to write the check myself but was rushed and did it wrong so the check reader denied my check. I do have the receipt and check I tried to write but that stores employees should be secretly investigated because the medicine I take make me kinda drowsy at night and they must of thought I was messed up but if u don’t investigate them now ur store will lose money or a customer will when they try to scan another person’s chip card with their phone they leave on the counter