1. Record it
Record the fact of the breach: an act, the correspondence, photographs, an expert opinion. An oral complaint is hard to prove later.
2. Send a claim
A claim takes written form. State the circumstances, the evidence, your demand, the sum and its calculation. Send the claim by registered letter, or hand it over against a receipt, and keep the proof of delivery. A business entity must answer the claim within 15 days from the day it receives the claim.
3. What you can demand
Performance of the obligation in kind; a penalty (a fine or interest for late payment); compensation for the losses (article 324 of the Civil Code); on a material breach of the contract — termination of the contract through the court and compensation for the losses that the termination causes.
4. The court
A dispute between business entities goes to the economic court. If the answer to the claim is a refusal, or no answer comes within the set time, you can file a statement of claim with the economic court. If the contract sets a procedure for the settlement of disputes, follow it.