Only way to find out is to phone up - as you sound to be in a fixed term, that'll be linked to expiring discounts, your costs will certainly go up (plus the 6-9% standard price rise effective from April). If your discount's a particularly good one you could be looking at a doubling of your bill. 😢
If you're feeling brave, then phone up and cancel now (well, start your 30 days notice), and wait for the outbound retention calls to arrive. If you're well prepared and know what competitor deals are out there, you can get new customer pricing or near enough via those outbound retentions calls, it's much more difficult to negotiate that on an inbound retentions call. Obviously you're banking on the outbound retentions call arriving - what if you miss them? You can always phone in 48 hours before your cancellation takes effect and then haggle, and take the best deal they'll offer on that day. In any conversation with a retentions agent (1) You can't leave a deal on the table whilst you mull it over - you immediately accept an offer if it's good, it won't be held open if you call back after thinking about it. (2) Loyalty, fairness mean nothing, those concepts are for weenies. All that counts is the prospect that you could seriously take your business elsewhere, and you know what great deals you can get from competitors.