Lumpy milk

I have been using nestle nido 3plus for a while now without any problems up until recently when i found a few lumps in the milk like it got moisture into it i then thought i probably put a wet s**** into the milk which caused it to lump i then scooped the lumps out and continued to use the milk but this morning when reaching near the bottom i found more lumps i then decided to feed it to my daughter and throw it away can you please explain what these lumps are? Is it still safe for consumption? There is no dampness in our house and i always keep the lid tightly sealed on so the lumps could not have happened in our house please explain nestle at R225 a 1.8 kg tin its expensive to throw away milk