This is a lot to read but it might help you
If by D(D)OS-ing me you mean somebody stealing your internet to slow yours down their are several things you can do.
1. set up your internet up so that nobody can use your hub/modem without inputting the keycode into their device , example , if YOU buy something new you should not be able to go on the internet through your hub unless you give the device access by inputting the key code.
2. go onto an online game and look at something called the latency figures and see if they suddenly change , if you dont have a game that can do this go onto an online game and look in task manager at the figures for your internet usage , when you notice a slow connection look at the task manager again to see if the internet figures have gone up. If they have it means 1 of 2 things , either you have something connecting to the internet that you dont know about or somebody is stealing your connection.
3. i dont know what av you have but i use the ESET paid for and it has something called network inspector.
Download the free version from here.
https://login.eset.com/login
Yes you have to set up an account but do it. Download the free trail version but before you install it disable your own av because you should not have 2 av running. Once installed run the network inspector part of the software .... dont do it when your internet is so called super slow , it will find everything going through your hub/modem. When your internet goes slow do it again and see if their is anything new on the list. If their is then somebody is using your connection.
4, if option 3 gets a result contact your isp.