If you're talking about your own home broadband wireless signal then nothing that your ISP is doing will have any effect on your wireless signal. Your router can broadcast a wireless network signal even if it's got no internet connection being piped into it.
If nothing about the router has changed but the signal strength has then it could be being affected by a neighbouring wireless network. Download inSSIDer for free
http://www.metageek.n...ts/inssider/download/ and use it to check for other wireless networks. Go into your wireless router's settings menu and make sure it's set to use a channel that's least populated (selecting channels 1,6 or 11 is best as these are the only ones that do not overlap). Report back your findings.