Am I my neighbor's hotspot?

I suspect that a neighbor is using my broadband cable connection as a free hotspot wireless connection for her. I have to pay 50 dollars a month for my connection. I am below poverty level and disabled. It's the only way I can see my kids and grandkids so far away.

 

I think my computer is slow at times because of her usage.

 

She is somewhat unsavory and if she does something bad while I my connection I could get blamed, right?

 

How do I lock down my computer so that nobody can use it for a wireless hotspot.

 

Easy instructions please I am not very tech savvy. Also..my router didn't come with a book or anything, I pay the cable company to rent it and it doesn't even have an on off button.

 

I contacted my cable company and they said it's a computer problem and to take it in and have it looked at.

 

they just want their money they don't give too hoots in hades about their customers I think.

 

help please? again, please?

 

Paula