Yoe need to understand the arithmetic of pcr to understand the difficulties. Every 10 cycles of pcr is 1000 times more product and 20 cycles is 1,000,000 times more product. This means that tiny amounts of post pcr product will produce huge amounts of new product. Contamination can be invisibly small amounts of dna.

I would order all new reagents . Strip down and wash all pipettes and get new plasticware. When the new reagents arrive move to another researchers working area and use their pipettes to make up new reagent stocks and then set uop the pcr on their pcr machine and with their pipettes. Meanwhile clean up your working area with soapy water and discard all plasticware. If your pcr with no template controls works as it should then move back to your area and set it up again with your pipettes and pcr machine.

Do not bring used gels back into your working area as the gel and buffer carry contamination.

If you still have contamination then design 1 new primer outside of your current primer set ( make a larger pcr product) then the old contamination cannot amplify and the problem will go away but it will return if you bring things back from the gel running area into your pcr setup area.

Also be very careful not to create aerosols when opening the caps/sealing tape on your pcr tubes which can often spread contamination.

Do not worry where your contamination is coming from at this time.....just order all new reagents and thoroughly clean pipettes and working area and get back working as soon as possible

Toss ALL of you reagents (except your RNA or cDNA). I mean ALL of them - water, buffers, primers, etc. If you've put a pipet tip in the container, it could be contaminated.

Clean your bench & pipettes. Get all new boxes of tips, new bag of PCR plates/tubes.

Try setting up just the positive and negative control reactions. Once those are working, then set up your experimental reactions.

The goal is to get rid of the contamination, not to track down the source.