optimization - Writing constraint in CPLEX OPL -

i have problem in writing constraint. have 1 mobile phone number, 4 tariff package , 9 months. now, solution giving different tariff each month. write constraint solution gives same tariff each model

    //data  {string} numbers = ...;//mobile phone number, id, 1 number  {string} usagecategories = ...;//{"fixed""mobile""international""data"}   tuple packageinfo {      string name;     float price;     float fixedminutes;     float mobileminutes;     float internationalminutes;     float data;   };   {packageinfo} packages = ...;//tariff package info   float usagefixed[numbers] = ...;//fixed min used  float usagemobile[numbers] = ...;//mobile other min used  float usageinternational[numbers] = ...;//international numbers used  float usagedata[numbers] = ...; //data traffic (kb)  float taxfree[numbers] = ...; //tax free items  float internationalservices[numbers] = ...; //international services  float priceperminute[usagecategories] = ...;//price per minute after minutes included in package   //minutes included in package each number...calculated in execute block overagefactor  float overagefixed[numbers][packages];  float overagemobile[numbers][packages];  float overageinternational[numbers][packages];  float overagedata[numbers][packages];     //decision vars  dvar boolean assign[numbers][packages];    //overage amount  execute overagefactor {      (var n in numbers) {         (var p in packages) {             if (usagefixed[n] < p.fixedminutes)                 overagefixed[n][p] = 0;             else overagefixed[n][p] = usagefixed[n] - p.fixedminutes;              if (usagemobile[n] < p.mobileminutes)                 overagemobile[n][p] = 0;             else overagemobile[n][p] = usagemobile[n] - p.mobileminutes;              if (usageinternational[n] < p.internationalminutes)                 overageinternational[n][p] = 0;             else overageinternational[n][p] = usageinternational[n] - p.internationalminutes;               if (usagedata[n] < p.data)                 overagedata[n][p] = 0;             else overagedata[n][p] = usagedata[n] - p.data;              }        }  };   dexpr float packagescost = sum (n in numbers, p in packages) p.price * assign[n][p]; //package cost   //overage costs  dexpr float fixedoveragecost[p in packages, n in numbers] =                                      overagefixed[n][p] * assign[n][p] * priceperminute["fixed"];  dexpr float mobileoveragecost[p in packages, n in numbers] =                                     overagemobile[n][p] * assign[n][p] * priceperminute["mobile"];  dexpr float internationaloveragecost[p in packages, n in numbers] =                                      overageinternational[n][p] * assign[n][p] * priceperminute["international"];  dexpr float dataoveragecost[p in packages, n in numbers] =                                      overagedata[n][p] * assign[n][p] * priceperminute["data"];   dexpr float cost = packagescost + sum (p in packages, n in numbers)                             (fixedoveragecost[p,n] + mobileoveragecost[p,n] + internationaloveragecost[p,n] + dataoveragecost[p,n])                        + sum (n in numbers) taxfree[n]                        + sum (n in numbers) internationalservices[n];   //objective  minimize cost;     //constraints  subject {      //one package each number     forall (n in numbers)         sum (p in packages) assign[n,p] == 1;      //every month same package      ?????????????????????????   };    //data display  tuple assignedpackage {     string id;     string package;   };   {assignedpackage} assignedpackages = {<i,p.name> | in numbers, p in packages : assign[i,p] == 1};   execute datadisplay {     writeln ("assign following packages users:");     (var in assignedpackages)         writeln (i);   }   current solution:   <"7" "vpn za sve s">  <"6" "vpn za sve l">  <"8" "vpn za sve s">  <"9" "vpn za sve s">  <"10" "vpn za sve l">  <"11" "vpn za sve m">  <"12" "vpn za sve m">  <"1" "vpn za sve s">  <"2" "vpn za sve m">