I'm having trouble with the code where the budget variable wasn't deducting throughout the loop. It instead do nothing or sometimes add up - queue

Question

enter image description hereI'm making an inventory system code and I'm a bit stuck finding a solution to the substraction problem, when I choose "ADD" and entering the input the formula wasn't getting the accurate outcome. For example, if I input Paper001 then its quantity, the output is fine at first but when input another item, the deduction instead becoming addition or sometimes doesn't do anything.
I tried dividing the values in the dictionary in 3 conditions but it turns out even worse.
while True:
try:
bg = float(input("Enter your budget : "))
print("-----------------------------------------------------------")
print(" Item name Item code Item price(Per set) \n")
print("1.Bond Paper : Paper001 100 PHP\n2.Yellow Paper : Paper002 50 PHP\n3.Intermediate Paper : Paper003 20 PHP\n\n")
s = bg
except ValueError:
print("PRINT NUMBER AS A AMOUNT")
continue
else:
break
a ={"name":[], "quant":[], "price":[]}
# converting dictionary to list for further updation
b = list(a.values())
# variable na value of "name" from dictionary 'a'
na = b[0]
# variable qu value of "quant" from dictionary 'a'
qu = b[1]
# This loop terminates when user select 2.EXIT option when asked
# in try it will ask user for an option as an integer (1 or 2)
# if correct then proceed else continue asking options
while True:
try:
print("-----------------------------------------------------------")
ch = int(input("1.ADD\n2.STORAGE LIST\n3.Customer purchase\n4.EXIT\nEnter your choice : "))
except ValueError:
print("\nERROR: Choose only digits from the given option")
continue
else:
# check the budget is greater than zero and option selected
# by user is 1 i.e. to add an item
if ch == 1 and s>0:
p_list={'Paper001':100,'Paper002':50,'Paper003':20}
pn = input("Enter item code : ")
if pn in p_list.keys():
q = int(input("Enter quantity : "))
else:
print("-----------------------------------------------------------")
print("Code is invalid")
continue
#checks if item name is already in the list
if pn in na:
ind = na.index(pn)
# remove quantity from "quant" index of the product
qu.remove(qu[ind])
# new value will be added to the previous value of user's quantity
qu.insert(ind, q)
tpr = (q+q)*p_list[pn]
print(f" Total product price:",tpr)
s = bg-tpr
print("\namount left", s)
else:
# append value of in "name", "quantity", "price"
na.append(pn)
# as na = b[0] it will append all the value in the
# list eg: "name"🙁"rice"]
qu.append(q)
# after appending new value the sum in price
# as to be calculated
tpr = q*p_list[pn]
print("\nTotal product price:",tpr)
s = bg-tpr
if s==0:
print("No more budget left")
print("\nAmount left :", s)
elif s>0:
print("\nAmount left :", s)
else:
print("Insufficient budget. Cannot buy item.")
print("Please restart and re-enter your budget.")
break
elif ch ==2 :
print("\n\n\nStorage list")
print("Item name Stocks ")
for i in range(len(na)):
print(f"{na[i]} {qu[i]}")
continue
elif ch == 3:
print("-----------------------------------------------------------")
p_list={'Paper001':100,'Paper002':50,'Paper003':20}
print("\n\n\nStorage list")
print("Item name Stocks ")
for i in range(len(na)):
print(f"{na[i]} {qu[i]}")
co = input("\nEnter customer's order : ")
if co in p_list.keys():
q = int(input("Enter quantity : "))
sl = qu[i]-q
print("Item is sold!")
print("Stocks left :",sl)
if sl <=0:
print("Please add new items!")
else:
print("-----------------------------------------------------------")
print("Code is invalid")
continue
elif ch==4:
print("")
print("\nThank your for shopping with us!")
break
elif s==0:
print("NO BUDGET LEFT. UNABLE TO ADD ITEMS.")
else:
print("ERROR: Choose only the digits given from the option.")