You have to have a corresponding bank statement for each pay slip. A letter if explanation will not be adequate. You should reschedule your biometrics and as stated, get the bank to print recent transactions and verify it.
This is what FM-SE says:
2. In respect of salaried employment in the UK (except where paragraph 9 applies), all of the following evidence must be provided:
(a) Payslips covering:
(i) a period of 6 months prior to the date of application if the person has been employed by their current employer for at least 6 months (and where paragraph 13(b) of this Appendix does not apply); or
(ii) any period of salaried employment in the period of 12 months prior to the date of application if the person has been employed by their current employer for less than 6 months (or at least 6 months but the person does not rely on paragraph 13(a) of this Appendix), or in the financial year(s) relied upon by a self-employed person.
(b) A letter from the employer(s) who issued the payslips at paragraph 2(a) confirming:
(i) the person’s employment and gross annual salary;
(ii) the length of their employment;
(iii) the period over which they have been or were paid the level of salary relied upon in the application; and
(iv) the type of employment (permanent, fixed-term contract or agency).
(c) Personal bank statements corresponding to the same period(s) as the payslips at paragraph 2(a), showing that the salary has been paid into an account in the name of the person or in the name of the person and their partner jointly.
