This has been a recurring theme with Lumix cameras. I bought my GH3 on Black Friday 2014 for a net £275, followed by my G7 on Black Friday 2015 for a net £250. The GH3 had already been replaced by the GH4 at the time but the G7 was a current model when bought. The cash back was delayed on both occasions and not provided in the stated timescale, but did finally arrive after a flurry of emails.
I'd love to have the IBIS on the GX80 but can't do without a mic input, I'll have to wait until the G80 is down in price.