Genuinely, if they’re lasting two weeks then stop putting them out – they’re going mouldy because they’re not being eaten. Try something else – put up a fat ball feeder, try sunflower hearts instead or niger seed instead. Different birds like different feed, and the accepted wisdom is not always right – for instance accepted wisdom is that goldfinch like niger seed. Well in our garden, they will hit the sunflower seeds like they’re crack cocaine. I can fill two feeders every day at busy times. You might need different feeders, as niger seeds will just fall out of a peanut feeder etc.
Also consider location – if the feeder is hanging on it’s on own in the middle of a vast open expanse, then birds wil shy away unless desperate because they don’t want the exposure. Our feeder is about 3 feet from the hedge and the sparrowhawk will still take a bird every week or two, any further away than that and the birds simply don’t have the opportunity to get to cover in case of danger
Another point, discourage cats. our bird life exploded when the neighbour’s cat died.
Three sacks a month?My seed gets gobbled up a lot faster than that.
We go through about a sack a month. It’s a 12.5kg sack of sunflower hearts though