My mother in law came to stay with us and 1 wk after she left I found a cockroach in my bathroom. Does that mean there’s more. Also the room she stayed in is right by the bathroom and where she was at before staying with us is infested with cockroaches. What do I do?

I opened a can of my favorite brand of sardines only to find a cockroach floating in the oil. This is a canadian brand distributed by an american company. I’m thinking about what is the right thing to do. Should I complain directly to the company, to the distributor or should I get a lawyer and sue them all?