Yeah, that's ********. It isn't a rebate in any sense of the word. We don't hand over money and then get some given back. We only ever pay the reduced amount. A better term is 'discount' although 'abatement' or 'correction' are equally as good.
Politicians like the term 'rebate' because it makes it look as if we're getting something back, but we don't.
However it's referred to it is definitely not true that "We send the EU £350million a week"
http://www.europarl.europa.eu/thinktank/en/document.html?reference=EPRS_BRI(2016)577973