@Khalique The SP customer information is very poor, but you can check with your bank if you paid the £100 twice, you can believe what your bank tells you, but not always believe what the SP app says.
@George3157 Hi, so not to leave you hanging , We cannot do anything with your account as we are just customers like you. You must continue with contacting SP with phone or email firstname.lastname@example.org
One certain , hassle free way of getting a refund is to go to the government website Gov.uk
and select "make a money claim online", make your claim for the amount owed, you have to pay a fee
but add that fee to the claim. If the claim is correct they should pay within 14 days, if the claim is incorrect they may challenge it and actually go to court, in this case you will have their immediate attention and obtain the correct amount.
the advantage of this method is that you let the court do the work, and do not have to spend ages on hold on the telephone, waiting for promises which are never kept nor waiting for replies to emails. Stress free!