Breaking up can be scary, but in most cases, you can cancel with your current provider over the phone or email.
If you're out of contract, you generally don't have to worry about the cost of cancelling your current service, but you'll likely need to give 30 days' notice.
Watch out for any hidden fees - check with customer services or have a look over the T&Cs to see exactly how much it would cost to cancel your current service.