Sometimes even big providers can suffer Major Service Outages (MSO) and thus it's not uncommon for support departments to become clogged up with related requests. Most people may only contact their ISP when exactly this sort of incident occurs, so if you can then it's wise to hunt out your ISPs Service Status, Twitter or Facebook page in order to check if there are any problems affecting your area first.
Example - Service Status Pages for the Biggest ISPs
BT
Service Status: https://btbusiness.custhelp.com/app/service_status_consumer
Twitter: https://twitter.com/BTCare
Facebook: http://www.facebook.com/BTUK
Sky Broadband
Service Status: https://servicestatus.sky.com
Twitter: https://twitter.com/SkyHelpTeam
Facebook: http://www.facebook.com/sky
TalkTalk
Service Status: http://www.talktalk.co.uk/service-status/
Twitter: https://twitter.com/TalkTalkCare
Facebook: http://www.facebook.com/TalkTalk
Virgin Media
Service Status: http://www.virginmedia.com/help
Twitter: https://twitter.com/virginmedia
Facebook: http://www.facebook.com/virginmedia
Failing that it's advisable to look around the Internet and see if there are other customers with the same problem. Community forums, such as the one on ISPreview.co.uk and other websites, are a good way of sharing concerns and getting answers to difficult problems.
The last option is to switch provider (new migration rules), which can be done simply by contacting the new ISP (no need to engage your old provider). But make sure you understand the implications of any early leaving fees or contract terms before doing so, although if you do get hit with unfair charges then these can always be tackled later through an ADR Complaints Handler.