Bosch Washing Machine Leaves Detergent on Clothes and Service Blames Me

We have a Bosch washing machine with dryer functionality, but when we wash our clothes and our baby's clothes, they come out with detergent residue. We immediately called Bosch, and they redirected us to their authorized service. The technician came and claimed we were using the wrong detergent. I pointed out that the user manual does not mention any restriction on this detergent. Then, in an attempt to justify a service fee, he said the detergent packaging recommends using one cup. I responded that the detergent company might write that to sell more, and he immediately left without providing any service document and later sent an IBAN number for the payment. Dear Bosch authorities, the information provided was insufficient, and I refuse to pay a service fee for an issue that is not our fault, especially since our washing machine is still under warranty. Please contact me for further details.