SQL & PL/SQL

Following the advice I got from my last  topic I have now  created my tables and now I want to populate them with my data but I get errors

below is my full sql command. From last time I learned that one foreign key can be implemented in one table and cannot be duplicated

to work around this I changed my foreign key as you can see to "fkone" . but why am I getting errors when trying to add information

I mean I have not gotten errors in the first two tables so what am I "doing wrong/ not understanding"

CREATE TABLE CUSTOMER (
CUSTOMERNAME varchar (25),
STREET varchar (25),
CUSTOMERCITY varchar (25),
CONSTRAINT CUSTOMER_pk PRIMARY KEY (CUSTOMERNAME));

CREATE TABLE DEPOSIT (
CUSTOMERNAME varchar (25),
BRANCHNAME varchar (25),
ACCOUNTNUMBER int,
BALANCE decimal (7,2),
CONSTRAINT DEPOSIT_pk PRIMARY KEY (ACCOUNTNUMBER));

CREATE TABLE LOAN(
CUSTOMERNAME varchar (25),
BRANCHNAME varchar (25),
LOANNUMBER int,
AMOUNT decimal (7,2),
CONSTRAINT LOAN_pk PRIMARY KEY (LOANNUMBER));

CREATE TABLE BRANCH (
BRANCHNAME varchar (25),
BRANCHCITY varchar (25),
ASSETS decimal (7,2) ,
CONSTRAINT BRANCH_pk PRIMARY KEY (BRANCHNAME));

ALTER TABLE DEPOSIT
add CONSTRAINT fk_BRANCH
FOREIGN KEY (BRANCHNAME)
REFERENCES BRANCH (BRANCHNAME)
ON DELETE CASCADE;

ALTER TABLE DEPOSIT
add CONSTRAINT fk_CUSTOMER
FOREIGN KEY (CUSTOMERNAME)
REFERENCES CUSTOMER (CUSTOMERNAME)
ON DELETE CASCADE;

ALTER TABLE LOAN
add CONSTRAINT fkone_BRANCH
FOREIGN KEY (BRANCHNAME)
REFERENCES BRANCH (BRANCHNAME)
ON DELETE CASCADE;

ALTER TABLE LOAN
add CONSTRAINT fkone_CUSTOMER
FOREIGN KEY (CUSTOMERNAME)
REFERENCES CUSTOMER (CUSTOMERNAME)
ON DELETE CASCADE;

INSERT INTO BRANCH (BRANCHNAME,BRANCHCITY,ASSETS) VALUES ('YORKSHIRE','NOTTINGHAM','10000');
INSERT INTO BRANCH (BRANCHNAME,BRANCHCITY,ASSETS) VALUES ('MIDLANDS','NOTTINGHAM','20000');
INSERT INTO BRANCH (BRANCHNAME,BRANCHCITY,ASSETS) VALUES ('ROYALBANK','NOTTINGHAM','25000');
INSERT INTO BRANCH (BRANCHNAME,BRANCHCITY,ASSETS) VALUES ('HFE','DERBY','15000');
INSERT INTO BRANCH (BRANCHNAME,BRANCHCITY,ASSETS) VALUES ('SOUTHERN','DERBY','30000');

INSERT INTO CUSTOMER (CUSTOMERNAME,STREET,CUSTOMERCITY) VALUES ('JONES','VICTORIA','NOTTINGHAM');
INSERT INTO CUSTOMER (CUSTOMERNAME,STREET,CUSTOMERCITY) VALUES  ('PATEL','CHURCH','NOTTINGHAM');
INSERT INTO CUSTOMER (CUSTOMERNAME,STREET,CUSTOMERCITY) VALUES  ('SMITH','DERBY','LEICESTER');
INSERT INTO CUSTOMER (CUSTOMERNAME,STREET,CUSTOMERCITY) VALUES  ('AHMED','CHURCH','DERBY');
INSERT INTO CUSTOMER (CUSTOMERNAME,STREET,CUSTOMERCITY) VALUES  ('BRAUN','ALFRED','DERBY');
INSERT INTO CUSTOMER (CUSTOMERNAME,STREET,CUSTOMERCITY) VALUES ('CHAN','VICTORIA','NOTTINGHAM');

Problems occur when trying to insert the following data into my tables

INSERT INTO DEPOSIT (CUSTOMERNAME,BRANCHNAME,ACCOUNTNUMBER,BALANCE) VALUES ('JONES','YORKSHIRE','1','100');
INSERT INTO DEPOSIT (CUSTOMERNAME,BRANCHNAME,ACCOUNTNUMBER,BALANCE) VALUES ('BRAUN','MIDLANDS','20','150');
INSERT INTO DEPOSIT (CUSTOMERNAME,BRANCHNAME,ACCOUNTNUMBER,BALANCE) VALUES ('AHMED','ROYALBANK','30','480');
INSERT INTO DEPOSIT (CUSTOMERNAME,BRANCHNAME,ACCOUNTNUMBER,BALANCE) VALUES ('SMITH','MIDLANDS','21','600');
INSERT INTO DEPOSIT (CUSTOMERNAME,BRANCHNAME,ACCOUNTNUMBER,BALANCE) VALUES ('PATEL','ROYALBANK','31','450');
INSERT INTO DEPOSIT (CUSTOMERNAME,BRANCHNAME,ACCOUNTNUMBER,BALANCE) VALUES ('PATEL','MIDLANDS','22','70');
INSERT INTO DEPOSIT (CUSTOMERNAME,BRANCHNAME,ACCOUNTNUMBER,BALANCE) VALUES ('BRAUN','SOUTHERN','41','2000');
INSERT INTO DEPOSIT (CUSTOMERNAME,BRANCHNAME,ACCOUNTNUMBER,BALANCE) VALUES ('JONES','HFE','42','4100');

ERROR at line 1:

ORA-02291: integrity constraint (N0430265.FK_CUSTOMER) violated - parent key not found

If your wondering what I am trying to achieve this is the given task I am meant to do. 

1. Add the following four tables to your
   database using the SQL statement CREATE TABLE (primary keys underlined) 

      Customer
      (customerName, street, customerCity) 

1. Deposit
   (customerName, branchName, accountNumber,
   balance) - where branchName and customerName are foreign keys to tables Branch
   and Customer. 
3. Loan
   (customerName, branchName, loanNumber,
   amount) - where branchName and customerName are foreign keys to tables Branch
   and Customer. 
4. Branch
   (branchName, branchCity, Assets). 

2.Add
the following rows of data to each table using the INSERT command: 

Thanks for taking your time to help I appreciate every feedback I get that can improve my SQL because I am getting into it and I want to ace my coursework