I think there are two types of non residents taxes you need to pay each year, one you can definitely do via direct debit, but you need to fill a form in. I'm pretty sure there's a council office now within Al Kazar next to Mileniun who can assist you. I can't remember how much it it is, both myself and my husband have to pay it as we don't live in Spain.
The other one (previously wealth tax) we do via our solicitors, or as Lizzie said you can do it via spanishtaxforms.co.uk.
You can also email Mileniun for advice at incidenciascondado@mileniun-levante.es
Their telephone number is 0034 968328024
Hope this helps,
Lynn