An experimental study of the low temperature magnetoresistance (MR) in a FeCl3-doped copolymer in which ethylenedioxythiophene and phenylene are alternatively linked by vinylene units is reported. The temperature dependence of conductivity followed characteristics of Coulomb gap variable range hopping (VRH) at low temperatures. The MR showed a crossover from negative to positive values. The crossover was explained by competition of negative and positive contributions which originated from quantum interference and shrinkage of wave function, respectively.