Ok Do you have a copy of the guarantee to check the terms eg any limitation on the guarantee in terms of amount or time limit? It is common though for liability to last until the end of the term of the lease.
Are you the only personal guarantor, if not then are debts joint and several?
Has the lease been forfeited through the insolvency? What is it the leasing agents are claiming for, rent arrears or other sums as well? In any event, has anything been sorted so further sums are not accruing?
Was any rent deposit deed put in place which could provide a fund for arrears or any insurance policies? The receiver should deal with the companies assets as regards creditors so make sure you keep in close contact with them as regards any sums being requested from you.
Some general advice about insolvency here...
http://www.business-support-wales.gov.uk/pdf/I nsolvency.pdf