Will it be permissible for me to default on the payment as I feel that it is unjust as I should have received 3 free consultations

In terms of Shariah ruling, am I obliged to make payment to the following individual:

I went for a eye operation to a Muslim optometrist last year. The cost of such a surgery was R10,000. The conditions of such an operation was that after the operation was done, I would receive three (3) free consultations with the optometrist. I presume that the 3 consultations were part of the operation fees

I went for 2 of my 3 free consultations last year and delayed the final consultation to this year. After examining my eye, the optometrist indicated that I should pay him R300 for the consulatation. I indicated to him that this was my final free consultation and that it should be free. His response was that operation only covered a one year period after the operation and since one year had lapsed I should pay the consultation fees

It was never indicated to me that all consultations should be done in the first year of the operation. After my second consultation, the receptionist did indicate that I should come within 9 months, but when I requested a date she said it was still too early. Subsequently I forgot about the 3rd consultation and due to exams delayed the consultation till now

Will it be permissible for me to default on the payment as I feel that it is unjust as I should have received 3 free consultations