The 28 day period is a non statutory return period that Lidl have - if you just don't like the goods then you can return then unused/as new with you receipt to get a refund. This does not affect your statutory right to a repair, replacement or refund if the goods are not fit for the purposes sold as may be the case here. I don't think that you have waived any statutory rights by contacting Targa support. If you are concerned then ask the NCA at www.consumerconnect.ie to clarify.