MSJhan!
Your concerns are genuine. Yes! Combinations are not permitable in homeopathy but very widely used in homeopathy.
All classical homeopaths are very found of using combinations although they don’t accept.
Actually the way they use is totally different. They will not give you Ferrum phos and kali mur at the sametime. First they will give ferrum phos and then kali-mur, which is also a form of combination.
To understand this sentence, you need lot of study of homeopathy. Bye the way combination by rule is allowed in homeopathy. Hahnemann himself used combinations. For authenticatin you can consult divina. That’s I have also proved so many times.