Is it permissible to take money in excess of the product's price and sell products that do not belong to the company, claiming they are from it, even though the company does not object as long as sales meet the required target, and is it sufficient to donate the profits to atone for this action?

It is not permissible to take the difference between the company's price and your selling price without its permission. Such an increase for the agent constitutes treachery and unlawful consumption of wealth, as stated by scholars. It is also impermissible to sell other products in the company's stores without its permission, as this involves aggression, deception, and misleading the buyer. The existence of prohibited acts by former employees does not justify imitating them, and custom is not considered valid if it contravenes Islamic law. You must repent, return the price difference to the company, and seek their forgiveness. Remaining in the job is permissible on the condition that you cease engaging in prohibited acts.