How do I stop my bath towels from smelling of mildew?

I am already on my second set – having thrown away the last set because I couldnt get rid of the mildew odor – now it is happening again with my new set!! I wash them twice each week and tumble dry them immmediatley until they are very dry – and I hang them to dry after every use – so what am I doing wrong? I have no other mildew issues in my home. THANKS!

The Vinegar Method
Put your towels in the washing machine, using the hottest water available. Add one or two cups of white vinegar. Do not add detergent, fabric softener, or any other products at this time. Run the washer.
Leave the towels in the washer and wash the same load again just as you would normally with laundry soap. Again, use the hottest water available. Don’t use fabric softener or any other products.
Dry the load in the dryer using a high heat setting. Towels should be thoroughly dry when you pull them out. If they’re not dry, put them back in, or move them immediately outside and hang them in the sunlight.

The Ammonia Method
Put your towels in the washing machine.
Add a normal amount of detergent.
Use the hottest water available. Do not add fabric softener or any other products.
Watch for the rinse cycle and add one cup of sudsy or clear ammonia during the rinse cycle.
Let the washing machine finish.
Move the towels out of the washer immediately. Fully dry the load right away using normal dryer settings, or hanging on the line on a sunny day.

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