Soldato
The way I interpreted his post was that he gets 20 days holiday per year. On occasion they are forced to work bank holidays in which instance they receive double pay. It isn't clear if this situation would then result in an extra day holiday. Because of this OP believes he gets 20 days holiday but is entitled to 28. Employer believes he is entitled to 20. OP has talked to ACAS who agree that the minimum holiday requirement is 20 + 8. OP has been employed for less than 2 years.