Abstract: A computer implemented method of constructing a computer implemented knowledge base, of evaluating a plurality of invoices, of knowledge refinement and generation, as well as a computer implemented knowledge base for analyzing a plurality of invoices. The methods comprise receiving the invoices, semantic and logically analyzing them to identify the invoice items (parameters and algorithms of service providers, billing plans, user profile, consumption pattern and debits) and relations connecting them and construct the knowledge base. The knowledge base comprises a hierarchic taxonomy of billing plans related to services of any domain (telecommunications services, banking, insurance, utilities etc.) and a computer implemented generic invoice constructed in reverse engineering logic for simulating debits. Debit simulations are done in order to achieve: 1. recommendations for optimal billing plans. 2. Recommendations for possible detected billing errors. 3.