Window Balance UB 28 B

A quick learner from Florida says:
Hello,
Please find attached pictures of the original channel balancer from my window. The sash weight is 13.6 pounds. The sash measurement is 35 wide x 31 height. The stamp on the original balancer was 28B for one window. Another window in my house had a balancer with a stamp of 28C.

I tried to identify the proper balancer myself but believe I chose the wrong part because the balancers I received are too narrow. I received these:
(2) S800-29 : 29" Series 800 Channel Balance
(2) S800-29 : 29" Series 800 Channel Balance

Please help me identify the correct balancers. I need two of each type- 28B and 28C.
Also, what is the process to return the parts that did not fit?
User submitted photos of a window balance.
Profile picture of Tom
Tom from SWISCO responded:
Depending on the measurements of the balance of the shoe, will determine whether you will need our S380-29 or S385-29 channel balance. Get back to us and let us know if you need any further help.
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