If an ISP offers big first-term discounts to new customers, then there's a good chance that they'll renegotiate at the end of your term, but you shouldn't assume that. The smaller the provider, the less likely they are to have a dedicated retentions department.
Sometimes the easiest way to save money on your broadband and phone service isn't by switching to a different ISP. In fact many of the UK's largest providers op
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I always choose providers based on post-contract pricing, not the first term offer for new customers.