Wrong price shows up on front end

I tried to find help on other boards, because I did not think the problem would be the theme - but everybody who tried to help told me the same... it is the theme, contact the support. Kindly referenced to this board now I really need help.

It is www.hosen-shop-behr.com - a german store, so I have to use german market plugin and translation.
In the backend the price is correct - f.e. Levis 99,95 / (reduced) 74,99
Sometimes it shows up correct on the front end, but mostly it doesn't - it shows 83,99 / 62,98
First I thought it has to do with the tax - but if I calculate our 19% out, it still doesn't fit.

So I don't where or what the problem is and I hope to find somebody here to solve this.

Hello,

Could you please provide me with a back-end and FTP access via PM (click the “Private Message” text underneath my avatar) so that I may analyze it?

I've checked your other themes and the prices are the same, so it's not a problem with the theme.
Please install also any default WordPress theme, like Twenty Fifteen, check the prices and report the issue to the WooCommerce support.