Since you’re based in the UK, I assume you’re talking about an EASA registered aircraft. Within EASA, a service bulletin is not mandatory even so called by some aircraft manufacturers. So legally you don't have a problem yet. However there is a reason why it’s called mandatory and normally its safety related. Most of mandatory or alert SB’s will become an AD and then you are obliged to comply with.
Regarding “overlooked” I would like to mention that it isn’t the responsibility of a PART 145 organisation to schedule the maintenance, this is the obligation of the contracted CAMO.
If it was ordered by the CAMO,than you could go back to the maintenance company to discuss it with them.
Source EASA:
AMC M.A.301 - 7- Continuing airworthiness tasks
An operator or a contracted M.A. Subpart G (CAMO) approved organisation as applicable should establish and work to a policy, which assesses non-mandatory information related to the airworthiness of the aircraft.
Non mandatory information such as service bulletins, service letters and other information is that produced for the aircraft and its components by an approved design organisation, the manufacturer, the competent authority or the Agency.
ED 2007/001/R
ED 2009/006/R