Help with epplus formulas (Excel) c #

I'm doing an excel in which I made some formula, but when I take a cell that is the result of a formula, to use it in another formula it shows me in the cell literally the formula.

As it is highlighted in the colors yellow is the range of providers L , blue is the cell in the column O , and in green is the range of that there is in the K column that is called AMOUNT

This is the code:

  string SUMA_SI_MONTO = celda + ":" + comparativo.Cells[(columna1 + i), (columna + 2)]; // K7:K8 MONTO

                string SUMA_SI_PROVEE = celda_Final + ":" + comparativo.Cells[(columna1 + i), (columna + 3)];// L7:L8 PROVEEDOR

                comparativo.Cells[(columna1 + i + 1), (columna + 2)].Formula = SUMA;// PRECIO AUTORIZADO
                for (int q = 0; q < proveedor.ToList().Count(); q++) {

                    // =SUMAR.SI(T7:T46,W7,S7:S46)
                    string _SUMA_SI = "=SUMAR.SI(" + SUMA_SI_PROVEE + "," + comparativo.Cells[(provedor_cont - 4) + q, (cont + 6)] +"," + SUMA_SI_MONTO + ")";
                    comparativo.Cells[(provedor_cont - 4) + q, (cont + 7)].Value = _SUMA_SI; // =SUMAR.SI(L7:L9,O10,K7:K9)

                }

And apparently only the formula is concatenating me. I have to enter the editing mode of the cell and leave it to show me the result.

Someone who has happened the same to help me?
Thanks.