SolarCity is not sending us a promised replacement part and refuses to fix the issue...

SolarCity is not sending us a promised replacement part and refuses to fix the issue. Have a ten-plus year old solar installation (owned). Last November, we started receiving emails that our system wasn't reporting power. Called support, who ran on-line diagnostics and said the problem appeared to be our gateway router. Said they'd send us a new one (not enough staff for a service call). We've called repeatedly since then, because we have gotten no further response. They keep telling us that the part is "on back order" and that they'll send it when it is in stock. Once or twice, they said the part was available and they'd check on why it wasn't sent. Today, after another service rep told us the part was on "back order", we asked if new customers weren't getting installations because of this. The rep admitted that the part was in stock, but only available as part of a new installation. This makes no sense -- what if the "new installation" includes a defective part? Does the new customer then have an incomplete system because the part can't be replaced? All we want is for SolarCity to send us the part that was promised to us almost a year ago. T