See below from fso 2011 case studies - has similarities to your case and may assist.
The Complainants took out a mortgage with the Bank in October 2006. In October 2007 the Complainants decided to reduce the period of their mortgage and fix the interest rate for a period of 3 years on a portion of their mortgage.
Towards the end of their fixed interest rate period, the Complainants approached their branch of the Bank to enquire as to what options were open to them at the end of their fixed interest rate period.
The Bank informed the Complainants that three options were provided in their loan agreement and these were: take a further fixed interest rate term, switch to a variable interest rate or a switch to a tracker interest rate. The Bank pointed out the loan agreement stated this choice was subject to the prevailing interest rates.
The Bank went on to advise that it had ceased to offer tracker interest rates in 2008 and that consequently, the Complainants could not switch the portion of the mortgage on the fixed interest rate to a tracker interest rate as the tracker interest rate was not a prevailing rate.
The Complainants were unhappy with this decision as they felt contractually entitled to avail of a tracker rate.
While the Ombudsman accepted that the Bank was entitled to stop offering tracker rates as a product, he noted that the Complainants had only switched a portion of their mortgage to a fixed rate. The remaining portion of the Complainants' mortgage had remained on a tracker interest rate. Consequently, as part of the Complainants' mortgage was subject to a tracker interest rate, the Ombudsman was satisfied that this was a prevailing rate within the terms of the loan agreement.
Accordingly the Ombudsman directed the Bank to place the relevant portion of the mortgage onto the tracker rate currently applicable to the remaining portion of the mortgage, backdated to expiry of the fixed interest rate term.